I have come across a similar dilemma in the past and there`s no easy answer. You would have to test every option to be sure. In my case the PSU that blew was in a mate`s computer and I was able to replace it with a spare but as in your case no joy. I was then able to test the mouse and keyboard on another system - both were dead. Next the RAM - dead etc etc.
The computer was about 4 years old anyway and by the time we`d priced up the PSU, Motherboard, KB & Mouse, RAM plus installation we would have spent the best part of a new system. It was time to upgrade. We saved the Optical and Hard drive which now sits in a caddy as a backup.