Most likely the Power Suppy has failed. Running for any length of time without cooling would be fatal to it. You could test it by removing it, jumping the green wire to the black wire on the 20/24 pin connector, hooking a fan to a molex plug, and seeing of both fans spin when power is supplied.
However, you could also buy one from the local biggox rippoff store, try it out, and return it if that is not the problem. But it probably is.