I'm guessing the ram or cpu man, sometimes even the mobo's die. Now, the cpu and ram seem to be of good quality, so I'd try those parts onna diff mobo without the HD or anything connected. Cause yeah, you don't need that stuff to POST. Just have the PSU connected to the mobo, and the cpu and ram in there.
If you have a spare mobo laying around that supports socket A and DDR 400 ram? give it a go. If yours supports it? you could also try it there.
Btw, emachines aren't ALL that bad. They say emachines has the best customer support for a big computer brand company.. so that has to count for something.