Computer Shutdown

[Splint]

My friend's computer displays a message and then powers down. He asked me to come over and take a look. But I'm not that good with Hardware. I know I don't have enough information and can't even say what the message says but could you help me with some possibilities

Overheating ?
Bios related problem ?

Thanks in advance

[LP-SolidRaven]

Does it display a timer before it shuts down?
If yes you don't have to look far. Cause in that case it's likely our good old friend called W32.Blaster. Try installing antivirus software if he hasn't done so yet.
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Dilly dally, shilly shally.

[ClickFanatic]

It could be anything.
Cleaning the inside of the case carefully (removing dust) might be a good remedy against overheating.

Does it happen directly at start-up, or while the operating system (Windows?) is running?
If it is at start-up, then you're probably facing a hardware or BIOS related problem.
Damaged or incompatible RAM memory. Did your friend add or change RAM memory recently? You can try swapping some of the chips. Consult the motherboard manual for details.
Corrupted BIOS (resetting the BIOS might help, or check the motherboard manual).
Low power. The PSU (power supply unit) may be outdated or unable to provide the power required by the PC (this could be a result of newly added hardware that requires more power, such as a video card).

Many possibilities, as you can see. It might be useful if you could find out what the message says before it shuts down.
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If you can read this, my post is on an alternating background.

[Perpetual]

The message is the key to finding out your problem. Overheating does not give you a message, it simply shuts off without warning.

My guess is that it is a software issue. Could have a corrupt file, program, virus, spyware and tons of other things.

Im guessing the message it gives you says something like a vital process has been terminated and windows will now shut down. You can recreate that message from opening up task manager and killing every process like svchost.

If no spyware, virus or whatnot, then reinstalling OS should fix the problem. But I would save that as a last resort for when you get fed up with trying to find the specific culprit.
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God doesn't exist but I do