I am having a similar problem with my computer. Originally, what seemed to occur was that while running a program that accesses the hard disk to a great extent, (e.g. defrag, DeDupe, P5 render) the computer will go into what appears to be a sleep mode. However, in order to get the computer to come back on I have to unplug and replug the tower. When XP reboots sometimes I get a message about a serious error occurring and I have to reboot. On this reboot everything starts up fine. Lately, however, I have had it go to permanent sleep while being idle. I realize there could be many causes. However, I am fairly certain this problem is not virus related (I have done a hard disk wipe and complete reinstall with original disks and I have an updated NAV). I can fairly regularly cause the problem to occur with a program called DeDupe that looks for duplicate files on my hard drive. With the many most likelys written above where should I start to address this problem? By the time a try to replace the CPU, replace RAM, replace the power supply, and replace the motherboard I might as well get a new computer.