Re: PC Automatically SHUTSDOWN! please help
it's definately the cpu overheating man, don't burn out that sweet cpu. get some arctic silver 5 and make sure that heatsink is on correctly, and like charchris said that the fan is plugged in. try this, leave the side panel open so you can see the fan and heatsink when you turn it on, make sure the fan starts spinning. On my friends rig, the heatsink went on one way only because it would hit some trasistors on one side which you couldn't easily see and it clamped down and everything so he thought it was on right but it had the same problems as you.
EDIT: lol you beat me to it, but still, read what i said