Computer shuts down after some minutes

[plutomaniac]

If with Prime95 it does not shut down then it's not the cpu cooling. I'm not saying that 96 is normal in any way but it's not what causes the problem. My guess would now be that the power supply is not enough. If it's old then it might has "lost some watts". Or it could be malfunctioning under heavy load. How old is it? Does it still have warranty?