Hi guys. I've recently fixed my iMacs power supply which had gone bad. But when I plugged it back in and started it up I...

Hmm did you see if any of the capacitors on the logic board blew?? If not and they look fine then I think it possibly could just be the PSU.. But I'm not entirely sure. Look on eBay for a used PSU that you can get pretty cheap and give it a shot. I recently bought a PSU for my iMac G5 20' for $20 that works.