i had a similar problem with an old gateway computer of mine so i pulled out the CMOS battery for an hour then replaced it with a new one and let it sit overnight (i guess to let the battery start sending some juice around) but it booted right the next day. **NOTE: I say let it set overnight cuzz it wouldnt boot after i put the battery back in until the next day.**

If that still doesnt work i would say take everythign out of your comp except the stuff thats necessary to boot. (i.e. Vid card, hard drive, 1 stick of ram you know to be good etc.. only the essentials.) then if it boots add each component 1 at a time until it messes up.

[EDIT] If you have access also try another power supply. It may not sound like a PS issue but ive had comps with bad PS give strange errors randomly.