the motherboard might be dead or gpu, you said the psu died and if the system was on when it died the psu could have thrown a lot of wild voltages around, if you can barrow a spare gpu from some one to test that would be my advice.,
Or maybe cpu might be gone you I dont really know and its hard to tell without being there.
TLDR if you have spare cpu, mobo or gpu try them one by one in the rig
Good luck!