I have one computer that will do that on occasion. However, I know it's a screwy driver somewhere and just have never bothered to fix it. I do not use the PC all that much, and it's never for anything critical. It happens once maybe every few months.
Sometimes it's power, and fan related and the chip saving your board by powering off. Sometimes it's a simple driver issue. You just have to have the time and patience to dig through and find the conflict to fix it.
