Fix a Computer That Turns On and Then Off [How To]

Here's How:

1. Troubleshoot the cause of the beep code, assuming you're lucky enough to hear one. A beep code will give you a very good idea of exactly where to look for the cause of your computer turning off.
   If you don't fix the problem that way, you can always return here and continue troubleshooting with the more generic information below.
2. Verify that the power supply voltage switch is set correctly. If the input voltage for the power supplydoes 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.
3. 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.
4. 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.

1. Tip: If you do end up replacing the PSU, keep the computer plugged in for at least 5 minutes before you try powering it on. This gives time for the CMOSbattery to charge a little.
2. 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.
3. 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 all internal data and power cables
   • Reseat the memory modules
   • Reseat any expansion cards
   Note: Unplug and reattach your keyboard and mouse as well. There is little chance that either one is the cause of this problem but we shouldn't overlook them while we're reseating everything else.
4. 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!
5. 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.
6. 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 Videosmight come in handy as you're reinstalling your hardware.
7. 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.
8. 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.
9. Finally, if all else fails, you'll likely need to seek professional help from a computer repair service or from your computer manufacturer's technical support.
   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.

Tips:

1. 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.

Via : about.com