Yeah...the thing is, the other motherboard doesn't even chime. The motherboard thats in it now chimes, and comes up with an image, like I said, it just doesn't boot. (either it hangs on the Happy Mac, or KPs if I try to boot into OS X) Before I try the ATX hack, one thing I'm thinking - the early iMacs have a seperate power filter board on the bottom of the logic board tray. Maybe I ought to try swapping them around...if I still don't get any joy, its time to try the ATX hack. (despite the fact that I *really* don't want to if I can help it )