Probably not to much. If your computer wasn't running at the time the thing blew up, there's afaik little danger that any power surges messed up any of your mainboards components. Just try the new power supply (it will certainly cause no new damage).
This sort of thing can happen to older power supplies esspecially when they're used with newer hardware. It's just wear and tear of the thing. Luckily they're not that expensive
