Have you checked the capacitors on the MOBO? They get overloaded sometimes, be it from lightning or bad wiring.
I had a friend who had similar problems and it was attributed as such by the guy she took it too.
Unfotunately, unless you have advanced experience with circuitboard repairs, if that's the problem you need to buy yourself a new MOBO.
The guy over on this page says it's definitely a possibility.