My Computer turns itself off what should I do?

I recently upgraded my graphics card to an 8800gts and after I installed it I started playing oblivion and about an hour into playing my computer turned itself off. It then happened again while playing S.T.A.L.K.E.R. and Rainbow Six Vegas. First instinct was that the graphics card was over heating or faulty. But before opening my case again I decided to check for the basic stuff like spyware or viruses. So I ran spybot but the computer turned itself off again about 5 minutes into the scan. So i ran my norton anti virus and sure enough it happened again. Then the next day I tried burning a dvd and the same thing happened. Strange thing is I can leave my computer on idle for days without it happening.

I have been told it's either over-heating graphics card or my power supply. But the fact that it happens when i do things that don't require any real graphics power leads me to think it's the power supply.

What do you think?

My Computer turns itself off what should I do?photoshop

if you have the od graphics card try putting it back in uninstall new one

probably is power supply

My Computer turns itself off what should I do?symatec

There is a third possibility, the processor could be overheating. Make sure the fan is running on the processor heatsink.

If it is, then check the power supply. That would be the most likely problem, because the graphics card would overheat very quickly when playing a game.
Make sure that your cooling supply to the CPU is working properly. Then check all the fans for dust buildup blow them out with canned air. When I leave mine run for days on end I'm amazed how quickly dust builds up in the fans. If the CPU isn't cooling well it will shut the computer down to protect the CPU from damage. If the fans are clean and dust free in the power supply also, then start looking at your PSU as a possible cause. You may not have a large enough PSU to power the newer graphics card and all the other equipment that you have on your computer.

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