Is your computer turning off by itself immediately or at some point before the operating system loads? If so, you may be facing anything from an electrical short to a serious hardware issue.
Since there are several reasons that your PC might be shutting off by itself during the boot process, it's important that you step through a logical troubleshooting process like the one I've described below.
Important: If your computer is in fact turning on and staying on, even if you don't see anything on screen, see my How to Troubleshoot a Computer That Won't Turn On guide for a more applicable troubleshooting guide.
If you don't resolve the problem that way, you can always return here and continue troubleshooting with the more generic information below.
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 stay powered on.
Chances are your computer wouldn't power on at all if this switch is wrong but an incorrect power supply voltage might also cause your computer turn off by itself.
Check for causes of electrical shorts inside your computer. This is very often the cause of the problem when the computer powers on for a second or two but then powers off completely.
Important: It's very, very important that you spend the time necessary to inspect the inside of your computer for issues that can cause shorting. If you don't take the time to troubleshoot this possibility thoroughly you may end up missing a simple electrical short and instead performing costly hardware replacements later on for no good reason.
Test your power supply. Just because your computer came on for a few moments doesn't mean that the power supply unit in your computer is working properly. In my experience, the power supply tends to cause more problems than any other piece of hardware and is very often the cause of a computer turning off by itself.
Replace your power supply if it fails any of your tests.
Test the power button on the front of your computer's case. If the power button is shorting out or even just sticking to the case, it might be the reason your computer is turning off by itself.
Replace the power button if it fails your testing or if you suspect it's not working properly.
Reseat everything inside of your computer. Reseating will reestablish all of the connections inside your computer which may have wiggled loose over time.
Try reseating the following and then see if your computer stays on:
Reseat the CPU only if you suspect that it might have come loose or might not have been installed properly.
Note: I call this out separately only because the chance of a CPU coming loose is very slim and because installing one is a sensitive task. This isn't a big concern if you're careful so don't worry!
Start your PC with essential hardware only. The purpose here is to remove as much hardware as possible while still maintaining your computer's ability to power on.
- If your computer turns on, and stays on, with essential hardware only, proceed to Step 9.
- If your computer continues to turn off by itself, proceed to Step 10.
Important: This troubleshooting step is easy enough for anyone to complete, takes no special tools, and could give a lot of very valuable information. This isn't a step to skip if, after all the steps above, your computer is still shutting off by itself.
Reinstall each piece of nonessential hardware, one component at a time, testing your computer after each installation.
Since your PC powered on with only the essential hardware installed, those components are working properly. This means that one of the devices you removed is causing your computer to turn off by itself. By installing each device back into your computer and testing after each installation, you'll eventually find the hardware that caused your problem.
Replace the faulty hardware once you've identified it. These Hardware Installation Videos might come in handy as you're reinstalling your hardware.
Test your PC using a Power On Self Test card. If your computer continues to power off by itself with nothing but essential PC hardware installed, a POST card will help identify which piece of remaining hardware is to blame.
If you don't already own and are unwilling to purchase a POST card, skip to Step 11.
Replace each piece of essential hardware in your computer with a "known good" identical or equivalent spare piece of hardware, one component at a time, to determine which piece of hardware is causing your computer to shut off automatically. Test after each hardware replacement to determine which device is faulty.
Note: Most normal computer users don't have a collection of working spare computer parts at their disposals. My advice is to revisit Step 10. A POST card is not expensive and is a much more reasonable approach than stocking spare computer parts.
Unfortunately, if you're without a POST card and also without spare parts to swap in and out, you're left not knowing which piece of your essential computer hardware is faulty. In these cases you have little option than to rely on individuals or companies that do have these resources.
Note: See the last tip below for information on requesting more help via the PC Support forums here on this site.
Are you troubleshooting this issue on a computer that you've just built? If so, triple check your configuration! There is a significantly greater chance that your computer is turning off by itself 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 turning off by itself during the boot process? Let me know and I'd be happy to include the information here.
Is your computer still shutting off automatically even after following the troubleshooting above? Let a community of computer support enthusiasts help out! Post the details of your problem in the PC Support Forum. Be sure to tell us what you've already done to try to fix the problem.