My pc will boot up ok and run perfectly, but shuts itself down after a random amount of time. I'll be sitting there writing an email, or ripping a cd, and boom! - it's shutdown. It happens that suddenly, like the power's been turned off at the mains or something. It doesn't automatically restart, either.
In terms of hardware changes, a new motherboard has recently been installed, but i am using the same cpu and heatsink cooler that formed the heart of a stable system in the past. However, since this old system was taken apart when the old motherboard went knees-up, i used the opportunity to wipe off the old thermal paste and apply some high-grade Zalman's paste. Both changes - the new mobo and the new thermal paste - were implemented at the same time.
Since then, this problem has developed.
If i try to switch it back on immediately after it has shut itself down, it'll get only so far into the boot sequence, and then shut down again. If i try to switch it back on after that, it'll shut down even earlier in the boot up process. It has to be left a couple of hours before it will succesfully boot up and can be used again.
I think it's a heating problem. I've added additional system fans, but they've made not the slightest difference.
If anyone has any ideas/experience/information that could help, i'd really appreciate it.