Well, I know what the problem is now. Fried the motherboard. Swapped my PSU out with his new one and everything works fine on my computer. His motherboard is a microATX type. Mine's a little newer. Was led to believe that the PSU was backwards-compatible, but it's designed for ATX 2.2. So I'm getting him a new motherboard. Thanks for all the input, and sorry for wasting yous guys time.