If you know the spare GPU works, test it out on the P5Q. That'll let you rule out the GTX being the culprit on the board. I'm sure most of us are still wondering, have you tried each piece of RAM, in different slots? I put a 1GB stick of Crucial ram that was known to be good (bought it brand new, and had it running in my PC), put it into my mother's PC and it wouldn't boot, tried it in every slot, and nothing. It was even on the listed compatible for her board, and it would not budge. Brought it home, put it in my PC to see if it just randomly failed, and it booted right up.