Kind of a pain

so my buddy has a gateway ex4200-o9. it was having problems with power supply (it blew a circuit in the house after turning it on), so i told him it was shot after looking at it (not that much of a guru) this was a couple months ago. it still doesnt turn on, so we bought a new power supply for it, and hooked it up correctly. tried to turn it on, failed. im thinking its like the motherboard or something, but id just like to make sure.