The CPU fan? Are you overclocking in any form? If it's the CPU fan, it's probably overheating and shutting down. If it's the video card, probably the same thing. Could be a driver-related issue as well(if it occurs when the system us booting). Try unplugging all your hardware except the essentials to operate your machine. If you have an onboard video-card, use it. Another problem could be a loose\damaged RAM stick. Try to keep the list of hardware with potential problems low, and add as you eliminate hardware on the list, until you locate the hardware causing the problem.
Also, ground yourself before touching your hardware. Although, I'm not sure how tolerant the hardware these days are to static electricity.
There are two types of tragedies in life. One is not getting what you want, the other is getting it.
If you wake up at a different time in a different place, could you wake up as a different person?