^Agree with above, it might simply be a bad PSU. A single rail can, and usually does go bad on a PSU, leaving the other rail working, so even though you are seeing some power to the system, it is not supplying power to everything. Second thing, it may be the board. Motherboards are made up of many multiple parts, circuits, capacitors, and regulators that very well could have been low quality when the board was made, or have endured to many power surges, or whatever, but they do just "go bad" from time to time.
A processor is the very, very last thing to suspect, processors just don't go bad normally. You have to be doing something pretty outrageous, or plain stupid to kill a processor.