Maybe make sure there's no debris sitting in those front panel connectors, any bits of metal or anything conductive. Grab some canned air and blow it off. You can get momentary switch and some wire from a hardware store to fashion a better button for your setup. Or you could get one with a plug for the mobo headers for a buck or two on the intertubes.
Have you tried resetting your BIOS to optimized defaults? There may be some voltage or power regulation setting that's possibly gone wonky.