PC won't turn on: step-by-step diagnosis
Diagnose and fix the most common reasons a computer won't start or show any signs of life.
A PC that shows absolutely no sign of life — no lights, no fans, nothing on screen — is unsettling, but before assuming it needs a repair shop, it's worth ruling out the simplest causes, which are also the most common.
First: rule out the obvious
- Check that the power cable is properly connected at both ends.
- If the power supply has a switch on the back, make sure it's set to "I" (on).
- Try a different outlet or power strip, to rule out a problem there.
Important clue: if absolutely nothing happens when you press the power button (no lights, no fans, not even a click), the problem is usually the power supply or the electrical connection. If the fans spin but nothing shows up on the monitor, that's a different issue — see our guide on no image on screen.
Step-by-step diagnosis
1. Check the power supply
If you have another compatible power supply handy, that's the fastest way to rule it out. If not, check that every connector (the 24-pin to the motherboard and the 4/8-pin CPU connector) is properly seated.
2. Unplug non-essential peripherals
Disconnect external drives, printers, and any USB device other than the keyboard. Sometimes a faulty peripheral can prevent the system from starting at all.
3. Check the RAM
If you have multiple RAM sticks installed:
1. Power off and unplug the PC from the wall
2. Remove all RAM sticks except one
3. Try powering on with just that one stick
4. If it turns on, test each stick individually to find the faulty one
Warning: always unplug the power cable before opening the case, and touch an unpainted metal part of the chassis before touching any component to discharge static electricity.
4. Listen for beep codes
Some motherboards emit a sequence of beeps that identifies the problem (memory, graphics, etc.). Check your motherboard's manual to interpret the exact code, since it varies by BIOS manufacturer.
When to see a professional
If the computer still shows no sign of life after all this, the problem is likely the motherboard or the power supply — and that's the point where a proper diagnosis with specialized equipment beats guessing and swapping parts blindly.
Frequently asked questions
Do lit-up motherboard lights mean the power supply is fine?
They show that some power is getting through, but they don't guarantee the supply can deliver enough power under load. If there's a light but it won't boot, the power supply can still be the problem.
Could it just be the power button and not the PC itself?
It happens more often than you'd think. You can test this by briefly bridging the two "Power SW" pins on the motherboard with a screwdriver — unplug the PC from the wall before touching anything, and only plug it in to actually run the test.
Can a power outage damage the power supply?
Yes, especially without a surge protector or UPS in place. It's one of the most common causes of a PC suddenly refusing to power on after a blackout.