My computer won’t start

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Complete guide (2026) to diagnose and fix the problem in 5 minutes

A computer that refuses to start can quickly become a source of stress, especially when you need it to work, study, or simply browse the internet. Fortunately, most faults can be identified quickly with a few simple checks.

This complete guide gives you practical, easy-to-follow steps to diagnose the cause of the problem. Whatever the issue—electrical, hardware, or software—you’ll have everything you need to fix it effectively.

1. Basic checks to do immediately


1.1 Check the power connections

Before you think about a more complex fault, start by checking the connections. It may seem obvious, but a simple cable that isn’t properly connected is often the cause of the problem. 

Make sure that:

  • The PC’s power cable is plugged into a working wall socket
  • The monitor’s power supply is correctly connected
  • The HDMI, DisplayPort or VGA cables are properly inserted into the graphics card and not into the motherboard

👉 A poor contact or a loose connection can be enough to completely prevent the system from starting.



1.2 Test the power button

Press firmly on the “Power” button. Check whether anything happens: a light indicator, a slight fan noise, or a beep. 

If nothing happens:

  • Try using a different button if your case has one (Reset, for example).
  • If you’re experienced, test starting up by bridging the “Power SW” pins on the motherboard with a screwdriver.

👉 Warning: this last method is for advanced users only.



1.3 Try another wall socket

The problem could be with the wall socket itself. Plug your computer directly into another socket, without using a multi-socket adapter or an extension lead. These accessories can sometimes cause electrical interference.

👉 Tip: test the socket with a lamp or another appliance to make sure it’s working.

This photo shows the back of a desktop computer, with its input/output ports: HDMI, DisplayPort, USB, Ethernet, audio and power. It visually illustrates the essential step of checking the electrical connections during a PC start-up diagnosis. A simple cable that isn’t inserted properly, an HDMI connection plugged into the wrong output (such as the motherboard instead of a dedicated graphics card), or a faulty USB port can prevent the system from working correctly. This image reinforces the crucial preliminary advice: always start by checking the physical connections before suspecting a more serious hardware fault.

This photo shows the front of a TUF Gaming case, with the power button, the USB ports, and an accessible audio connector. It illustrates the power button verification step during a PC no-start fault diagnosis. If no LED lights up, no fans spin, or no sound signal is heard, it’s important to test the power button itself, or use the Reset button if present. If you’re unsure, you can consider manually starting via the motherboard’s Power SW pins (a method reserved for experienced users). This image reinforces the surface-level hardware check before considering internal interventions.

This image shows a standard power socket with a multi-socket adapter in the background, illustrating the check of the mains power supply during a PC start-up diagnosis. It’s recommended to plug the computer directly into a wall socket, without using a multi-socket adapter or extension lead, to avoid electrical interference or voltage drops. This photo completes the procedure visually by testing another socket using a working device such as a lamp, to rule out any fault that originates from the electrical supply.

1.1 Check the power connections

Before you think about a more complex fault, start by checking the connections. It may seem obvious, but a simple cable that isn’t properly connected is often the cause of the problem. Make sure that:

  • The PC’s power cable is plugged into a working wall socket
  • The monitor’s power supply is correctly connected
  • The HDMI, DisplayPort or VGA cables are properly inserted into the graphics card and not into the motherboard

👉 A poor contact or a loose connection can be enough to completely prevent the system from starting.


1.2 Test the power button

Press firmly on the “Power” button. Check whether anything happens: a light indicator, a slight fan noise, or a beep. If nothing happens:

  • Try using a different button if your case has one (Reset, for example).
  • If you’re experienced, test starting up by bridging the “Power SW” pins on the motherboard with a screwdriver.

👉 Warning: this last method is for advanced users only.


1.3 Try another wall socket

The problem could be with the wall socket itself. Plug your computer directly into another socket, without using a multi-socket adapter or an extension lead. These accessories can sometimes cause electrical interference.

👉 Tip: test the socket with a lamp or another appliance to make sure it’s working.

multi-socket adapter

2. Eliminate sources of physical conflicts


2.1 Unplug all USB peripherals

An external device may prevent the system from starting correctly. 

Disconnect all devices connected via USB: USB sticks, external hard drives, printers, headsets, webcams, etc.

👉 Some devices can cause a boot conflict, especially if the BIOS is trying to boot from an external drive.





2.2 Remove and test the RAM sticks

RAM memory sticks are often to blame when a computer won’t start. Here is the recommended procedure:

  1. Completely switch off the computer and unplug it
  2. Open the case
  3. Remove the RAM sticks one by one
  4. Replug in just one and try to start
  5. Then test with the other stick and change the slot if necessary

👉 A faulty or incorrectly installed memory stick can completely prevent the system from booting.



2.3 Check the graphics card connections 

If your PC has a dedicated graphics card, it’s possible that it’s not connected properly. Carefully unplug it, then plug it back in, making sure it’s fully seated in the PCI-Express port.

If your graphics card has a power supply cable, also check that connection.

👉 Tip: if your processor has an integrated graphics chip, you can connect your monitor directly to the motherboard to test booting without the dedicated graphics card.



2.4 Inspect the internal power cables 

Inside the case, check the power cables that go to the processor (CPU) and the graphics card (GPU). They may come loose partially during a move or a knock.

👉 Tip: use your smartphone’s torch to follow the cables from the power supply to the components. Reconnect them if necessary.

This image shows a computer workstation with a monitor, keyboard, audio headset, and visible USB cables, representing a typical user setup. It supports the recommendation to unplug all USB peripherals when troubleshooting a PC startup. USB sticks, external drives, or audio/video peripherals can interfere with system booting, especially if the BIOS is trying to boot from an external drive. This photo visually reinforces the importance of simplifying the configuration when trying to find the cause of a stuck startup.

This image shows the inside of a gaming PC, with two DDR5 Kingston FURY RAM sticks installed on an ASUS ROG motherboard, surrounded by sleeved cables and an RGB liquid cooling system. It illustrates the recommended memory diagnostic step when a computer won’t start. An incorrectly installed or faulty stick alone can be enough to prevent the system from booting. It’s recommended to test each module individually, switching DIMM slots if necessary, to identify any possible hardware defect. This check is simple to perform and helps quickly isolate the source of the problem.

This image shows a TUF Gaming NVIDIA GeForce RTX graphics card mounted on an ASUS motherboard, with its PCIe connector clearly visible and the power cables connected. It visually illustrates the essential check of the GPU connection when troubleshooting a PC that won’t start. A card that isn’t fully seated or a forgotten power cable can completely block the system. It’s recommended to remove and reinsert the graphics card, and to test booting via the integrated graphics chip if the processor supports it, by connecting the monitor directly to the motherboard’s video output. This image is ideal for reinforcing this hardware diagnostic procedure.

This image shows the neatly organised interior of a high-end gaming PC, equipped with an ROG liquid cooling system, RGB RAM sticks, a GeForce RTX graphics card, and several visible internal power cables. It illustrates the crucial step of checking internal connections to resolve a PC startup issue. The CPU (EPS 8-pin) and GPU PCIe cables must be firmly seated, because a move or poor handling can lead to a partial disconnection. Using a smartphone torch is recommended to follow the cables from the power supply to the key components, ensuring stable and continuous power.

2.1 Unplug all USB peripherals

An external device may prevent the system from starting correctly. 

Disconnect all devices connected via USB: USB sticks, external hard drives, printers, headsets, webcams, etc.

👉 Some devices can cause a boot conflict, especially if the BIOS is trying to boot from an external drive.


2.2 Remove and test the RAM sticks

RAM memory sticks are often to blame when a computer won’t start. Here is the recommended procedure:

  1. Completely switch off the computer and unplug it
  2. Open the case
  3. Remove the RAM sticks one by one
  4. Replug in just one and try to start
  5. Then test with the other stick and change the slot if necessary

👉 A faulty or incorrectly installed memory stick can completely prevent the system from booting.


2.3 Check the graphics card connections 

If your PC has a dedicated graphics card, it’s possible that it’s not connected properly. Carefully unplug it, then plug it back in, making sure it’s fully seated in the PCI-Express port.

If your graphics card has a power supply cable, also check that connection.

👉 Tip: if your processor has an integrated graphics chip, you can connect your monitor directly to the motherboard to test booting without the dedicated graphics card.


2.4 Inspect the internal power cables 

Inside the case, check the power cables that go to the processor (CPU) and the graphics card (GPU). They may come loose partially during a move or a knock.

👉 Tip: use your smartphone’s torch to follow the cables from the power supply to the components. Reconnect them if necessary.


3. Check the front panel and the Power button

The front panel—this small set of cables connecting the Power, Reset buttons and the indicator lights to the motherboard—can be responsible for a failure to start if it’s connected incorrectly.


3.1 Why the front panel can prevent the computer from starting

If the "Power SW" cable isn’t properly connected or is plugged into the wrong location on the motherboard, the power button won’t send any signal. The PC will remain off, even if everything else is working.


3.2 How to reconnect the cables correctly

Each motherboard has a specific area dedicated to connecting the front panel, often located at the bottom-right. Here’s how to proceed:

  • Refer to your motherboard manual (or search for an online PDF version)
  • Identify the exact location of each pin (Power SW, Reset SW, HDD LED, etc.)
  • Connect the connectors to the correct locations, observing the polarity if necessary

Once the cables are correctly installed, try restarting the computer.

  1. Completely switch off the computer and unplug it
  2. Open the case
  3. Remove the RAM sticks one by one
  4. Replug in just one and try to start
  5. Then test with the other stick and change the slot if necessary

👉 A faulty or incorrectly installed memory stick can completely prevent the system from booting.




This image shows in detail the front panel connectors on a PC case (Power SW, Power LED, HDD LED, Reset), plugged into the motherboard’s specific pins. Accompanied by a clear visual diagram, it perfectly illustrates the instructions given in sections 3.1 Why the front panel can prevent the computer from starting and 3.2 How to reconnect the cables correctly. A poor connection of the Power SW cable can completely prevent the PC from starting, even if the components are working. This image helps the user identify, orient and insert the front cables correctly, following the polarity and the pin positions, often located at the bottom-right of the motherboard.


3.1 Why the front panel can prevent the computer from starting

If the "Power SW" cable isn’t properly connected or is plugged into the wrong location on the motherboard, the power button won’t send any signal. The PC will remain off, even if everything else is working.

front panel


3.2 How to reconnect the cables correctly

Each motherboard has a specific area dedicated to connecting the front panel, often located at the bottom-right. Here’s how to proceed:

  • Refer to your motherboard manual (or search for an online PDF version)
  • Identify the exact location of each pin (Power SW, Reset SW, HDD LED, etc.)
  • Connect the connectors to the correct locations, observing the polarity if necessary

Once the cables are correctly installed, try restarting the computer.

  1. Completely switch off the computer and unplug it
  2. Open the case
  3. Remove the RAM sticks one by one
  4. Replug in just one and try to start
  5. Then test with the other stick and change the slot if necessary

👉 A faulty or incorrectly installed memory stick can completely prevent the system from booting.

  4. Your PC powers on but Windows won’t load?

If your computer turns on (lights, fans, noise), but the screen stays black or Windows won’t load, the problem is probably software-related.

4.1 Accessing Safe Mode

Safe Mode allows Windows to start using the bare minimum drivers. This can get around an issue caused by a faulty driver or malicious software.

Here’s how to access it:

  • Press the F8 key several times during startup (on some newer PCs, this no longer works)
  • Otherwise, forcibly restart your PC three times in a row to trigger automatic repair
  • Then click on “Advanced options” > “Troubleshoot” > “Advanced options” > “Startup Settings” > “Restart”, and choose Safe Mode.



4.2 Using Windows recovery tools

Windows includes several tools to repair a failed startup:

  • Automatic Repair
  • System Restore
  • Reset with keeping your files

You can access these tools via a bootable USB stick containing Windows, or directly from the recovery environment if it starts automatically.

Learn more

safe mode

4.1 Accessing Safe Mode

Safe Mode allows Windows to start using the bare minimum drivers. This can get around an issue caused by a faulty driver or malicious software.

Here’s how to access it:

  • Press the F8 key several times during startup (on some newer PCs, this no longer works)
  • Otherwise, forcibly restart your PC three times in a row to trigger automatic repair
  • Then click on “Advanced options” > “Troubleshoot” > “Advanced options” > “Startup Settings” > “Restart”, and choose Safe Mode.

safe mode


4.2 Using Windows recovery tools

Windows includes several tools to repair a failed startup:

  • Automatic Repair
  • System Restore
  • Reset with keeping your files

You can access these tools via a bootable USB stick containing Windows, or directly from the recovery environment if it starts automatically.

Learn more

5. Last resort: resetting the BIOS/UEFI

When all other checks have failed, resetting the BIOS (or UEFI) can be an effective solution for resolving a startup problem caused by a bad configuration or a system error.

When and why to reset the BIOS


The BIOS controls your computer’s startup. Incorrect settings (after a failed update, a power cut, or a handling mistake) can prevent your PC from starting. 

Resetting the BIOS restores the factory settings.

Methods for accessing the BIOS

There are two simple methods:

  • By Restarting with the SHIFT key : 
  • Click on the “Restart” button while keeping the SHIFT key (above CTRL) pressed in.
  • A blue menu will then appear. Select the option “ Troubleshoot ”.
    • Click on “ Advanced options ”.
    • Select “ Change UEFI firmware settings ”.
    • Click on “ Restart ”

  • Access the blue menu from Settings:
    • Click on the Windows logo at the bottom-left of the screen.
    • Open Settings by clicking on the gear icon.
    • Select “ Update & Security ”
    • In the left-hand menu, click on “ Recovery ”.
    • Under “Advanced startup”, click on “ Restart now ”.

Methods for resetting the BIOS

By dedicated button: some motherboard models have a “Clear CMOS” or “Reset BIOS” button. Check your motherboard manual to find it.

By removing the CMOS battery: switch off the computer, unplug it, open the case, and remove the round silver metal battery (type CR2032) located on the motherboard. Wait 5 minutes before putting it back.

Once the reset has been completed, reconnect all components and restart the PC.

Learn more

reset the BIOS

6. Common faults and quick fixes

Some faults are frequent and can be easily identified if you know what to look for.


Faulty RAM

This is one of the most common causes. Beep sounds during startup or a black screen with no signal may indicate a problem with the system memory (RAM). Test each memory stick separately in different slots to isolate the issue.


Motherboard not receiving power

If no lights come on, nothing moves and no sounds are made, the motherboard may not be getting any power. Check the 24-pin main power connector as well as the 4- or 8-pin connector to the processor.


Overheating problems or faulty fan

A faulty fan can prevent the computer from starting to avoid overheating. Open the case and check whether all the fans are spinning normally. Clean out the dust if necessary.

7. What to do if the problem persists?

If, despite all these checks, your computer still won’t start, it may be time to consider getting professional help.


Contact a professional

A technician will be able to carry out more in-depth tests: checking the motherboard, the processor, the internal power supply, or even more subtle issues such as short circuits.

This intervention can save you from buying replacement parts unnecessarily if the problem is identified quickly.

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