Built this simple system for wife and kid.

Gigabyte 7VKMLS ver 3.0
AMD Duron 1 gig processor
1 gig of memory
Two 20 gig hard drives
1 multi optical drive (DVD, CD, etc)
Windows XP home edition

System has always run well, until I noticed the CPU cooler fan had started to rattle. So I cleaned the heat sink fins, replaced the cooler fan, and fired her up. BUT after awhile, (usually 15-30 minutes), and after the screen saver has kicked in (5 min) the screen goes black, and the system will not respond. If I hit a key the HD light comes on, but that is about it. When I shut the system down, and try to reboot, I get absolutely nothing, no POST, nada. IF I let the system sit overnight, it will reboot the next morning. Checked in the BIOS hardware monitoring section, and CPU temp and speed never rise about 60 C, (shutdown is 110C). Checked Windows, and power scheme is set for nothing to shut down, ever (monitor, HD, etc), and it’s not set to hibernate. Problem did not occur until I opened the case and replace the CPU cooler fan.