I came across a Dimension E510 that appears to be possessed. Initially it powers up fine, but after about 30 minutes it shuts itself off. Then it turns itself on and off. The amount of time it rmains on varies each time. It even closes down some programs before shutting down. A few seconds later, it starts up all by itself. I was advised the modem could be messing up the bus, so I removed it. The problem remained. The system is about 18 months old and started doing this about 4 months ago. Any ideas?