Spontaneous Rebooting

I have a Asus P4B533-E motherboard with a P4-2.26G CPU, 2 Maxtor 40 Gig harddrives in a Raid 1 setup, running Win98SE for our office server. Recently the system began shuting off for no reason. I removed the Raid configuration and attached the maindrive to the IDE bus. Windows came up with windows protection errors, requiring reboots. I verified that the fans were all running and reseated the video card (the only card). I then reinstalled Win98SE. Everything worked fine for about 2 hours and the cycle started again. The case, power supply, motherboard and CPU are all less that 9 months old. Any ideas, suggestions, etc would be helpfull.