my second PC was working totally fine, and then i put a 'new' PSU in it (An old 420w i got off a mate) so it could power a new graphics card, the PC the failed to start, did nothing, although the Mobo's status light was on. so i took the psu out and put back in the old one. the fans now spin, the HDD is powers, the DVD drive opens, but i get no video output. not on chipset graphics and not on a GPU, im pretty sure the RAM is fine. same deal on two different motherboards. please help i really need this pc to work ps: the cpu is a core 2 duo LGA775 stock@ 2.0ghz