I had my computer do this awhile ago, but I had fixed it. My GPU fan wasn't spinning, causing it to overheat and then auto restart to prevent damage. This is no longer the issue as my graphics card fan is fully functional and my temperatures are now what seem to be normal. This isn't a gaming GPU, but I'm not really playing any stressful games. I have a AMD Radeon HD 6670 1GB, and I'm playing Minecraft. I downloaded a program to monitor temperatures and my graphics card never rises above 121* F while playing Minecraft. After awhile of playing Minecraft or any other mildly stressful application, my computer auto restarts. I know it is not my CPU, which never rises above 65* F. I cannot imagine what could be overheating, or if that is even the problem. No recent hardware changes, nor software changes. Please help; any and all is appreciated.
try running memtest86 from a boot cd or floppy or usb stick to see if you have a bad dimm. check that your dimms and power plugs are seated. try running hardware monitor and watch that the ps voltage is holding.
Thanks for all the help guys. I'll try to get a new PSU soon, since that the fact that its just not holding up makes sense to me. It's only a 500W, so I need an upgrade anyways. Just curious as to why I've had this computer for about eight months now, and that it acts up now.... Meh, its a cheapo PSU anyways.