I'm afraid the unit has a hardware problem. Power surges or instabilities of +/- 10/12% of the nominal voltage may be fatal to digital equipment. You may try reinitializing the unit, either with a CLEAR SETUP (doesn't erase your presets) or a FULL REINIT (kills your stuff!) and check if it helps.
Power w/SETUP key pressed & held for clear setup & follow screen instructions.
Power w/8 key pressed & held for full renit & follow screen instructions.
Please let me know!