No there is no danger of having too much in the way of power. Its when you have too little that the problems seem to arise.
I remember a while back you were wanting to build a new PC Hayashi. Now might be the time to learn the bit about how to do it. IF its your power supply you might just want to get a whole new case. IF you go to a market or swap meet of some kind many of the power supplies will be used anyway. You might be able to find one new and without a case but chances are youll have to buy a case as well if you want a NEW power supply.
All you have to do if you get a new case is take the old stuff out and remember how you did it. Back engineer it. Then just put it all together in reverse order. Its not hard at all. Once you do it youll have the confidence to do it again. Experience is the best teacher
It also could have been the CPU but yes it does sound more like a power supply.
Onething to keep in mind is that if it was the motherboard that went bad it could have fried the power supply when it went out of commision. Take it to a local tech and see what he says. And find out how much to replace any bad parts.