The motherboard probably died. 
Don't know if there's any way to fix it. You would have to inspect the motherboard up close.
This guide is for the SE/30, but I'm sure most of it will still apply.
http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#BlackOut
Some people have had success of reviving motherboards by running them through the dishwasher or cleaning the "capacitor corrosion" by hand with soapy water/rubbing alcohol. If you try this make sure you have rinsed it and let it dry completely before powering it. (Let it sit out in room temperature overnight.)
Don't know if there's any way to fix it. You would have to inspect the motherboard up close.This guide is for the SE/30, but I'm sure most of it will still apply.
http://www.biwa.ne.jp/~shamada/fullmac/repairEng.html#BlackOut
Some people have had success of reviving motherboards by running them through the dishwasher or cleaning the "capacitor corrosion" by hand with soapy water/rubbing alcohol. If you try this make sure you have rinsed it and let it dry completely before powering it. (Let it sit out in room temperature overnight.)