Among the many ways that a computer won't turn on, a complete loss of power is rarely the worst case scenario. There is the chance that your PC isn't receiving power because of a serious issue but it's unlikely.
There are several reasons that your computer won't power on so it's very important that you step through a complete troubleshooting procedure like the one I've outlined below.
Important: If it appears that your computer is in fact receiving power (you see lights on the computer case, fans are running, etc.), see my How To Troubleshoot a Computer That Won't Turn On guide for a more applicable guide.
Believe it or not, the number one reason why a computer won't turn on is because it wasn't turned on!
Before starting a sometimes time consuming troubleshooting process, make sure you've turned on every power switch and power button on your computer:
- Power button/switch on the front of the computer
- Power switch on the back of the computer
- Power switch on the power strip, surge protector, or UPS (if you have one)
Verify that the power supply voltage switch is set correctly. If the input voltage for the power supply does not match the correct setting for your country, your computer may not power on at all.
Check for disconnected computer power cable connections. A loose or unplugged power cable is one of the top reasons why a computer doesn't turn on.
Replace the computer's power cable. This is the power cable that runs between the computer case and the power source.
A bad power cable isn't a common cause of a computer not receiving power but it does happen and is very easy to test for. You can use the one that's powering your monitor (as long as it seems to be getting power), one from another computer, or a new one.
Perform a "lamp test" to verify power is being provided from the wall. Your computer isn't going to turn on if it's not getting power so you need to make sure that the power source is working properly.
Note: I don't recommend testing an outlet with a multimeter. Sometimes a tripped breaker can leak just enough power to show proper voltage on the meter, leaving you with the assumption that your power is working. Putting a real load on the outlet, like a lamp, is a better option.
Test your power supply. At this point in your troubleshooting, it's very likely that the power supply unit (PSU) in your computer is no longer working and should be replaced. You should however test it just to be sure. There's no reason to replace a working piece of hardware when testing it is fairly easy.
Exception: An ozone smell or very high pitched noise, combined with no power at all in the computer, is an almost certain indication that the power supply is bad. Unplug your computer immediately and skip the testing.
Replace your power supply if it fails your testing or you experience the symptoms I just described.
Important: In the majority of cases when a computer isn't receiving power, a nonworking power supply is to blame. I bring this up again to help stress that this troubleshooting step should not be skipped. The next few causes to consider aren't nearly as common.
Test the power button on the front of your computer's case. It's not a very common point of failure but your computer might not be receiving power because the power button on the front of your PC is damaged and is not actually turning your computer on.
Replace the power button if it fails your testing. Depending on how your computer's case is designed, you may be able to use the reset button in the meantime.
Tip: Some motherboards have tiny power buttons built in to the boards themselves, providing an easier way to test the case's power button. If your motherboard has this, and it works to power on your computer, replace the case power button.
Replace your motherboard. If you're confident that your wall power, power supply, and power button are working, it's likely that there is a problem with your PC's motherboard and it should be replaced.
Note: While perfectly doable by anyone with some patience, replacing a motherboard is rarely a quick, easy, or inexpensive task. Be sure you've exhausted all of the other troubleshooting advice I've given above before replacing your motherboard.
Note: I highly recommend that you test your computer with a Power On Self Test card to confirm that the motherboard is the cause of your computer not turning on at all.
Are you troubleshooting this issue on a PC that you've just built yourself? If so, triple check your configuration! There is a decent chance that your computer isn't powering on due to a misconfiguration and not an actual hardware failure.
Did I miss a troubleshooting step that helped you (or might help someone else) fix a computer that's not showing any sign of power? Let me know and I'd be happy to include the information here.
Is your computer still showing no sign of power even after following the steps above? Let a community of computer support enthusiasts help out! Post the details of your PC power problem in the PC Support Forum. Be sure to tell us what you've already done to try to fix the problem.