It seems like this is usually a motherboard problem but it could possibly be a overheating cpu. I'd re-seat CPU in the slot and make sure the pins are alright and then also carefully reseat HSF, on general principles since it appears at least to be a CPU issue, and if that don't work I'd look at mobo. perhaps you need a bios update if this is a new system?
Mine did the say today, I put a new ati 4850 graphics card and a fifth 1 terra bite hard drive in and it won't start, also went from 2 gig ram to 6gig ram and no dice. I stripped it down to bare bones and still won't run post. I am think pwer supply crapped with new gpu sent it over the edge? Any suggestions? robbie.foster@earthlink.net