I would suspect that the Compaq PSU is not compatible with your new motherboard. In fact you are lucky your motherboard hasn't fried. Your BIOS is probably looking for some kind of signal from the PSU that the PSU is not providing so the BIOS sees it as an error. Get a New case and PSU and make sure they are compatible. ATX Clone is the standard you want. I would cease running that motherboard off that PSU.