I am running windows 2000. This problem occurs only when computer starts after not being run for several hours, overnight, etc. The problem has moved as follows: 1. With the old power supply, I start the computer, and the bootup process gets up to the "starting windows" screen, then restarts. 2. With the new improved power supply (two fans), the process gets up to the desktop, and then restarts. In either case, after restarting several times, the computer completes the bootup process and runs fine. It seems like something needs to get warmed up before it will work properly.