Try the Self-Check Function :
Press VOLUME (-) button on The TV & SLEEP button on the remote simultaneously.
On the Screen Display, anything other that "OK" indicates a problem.
Press Channel + / - to exit.
NOTE: On the 60/600U Models The Self-Check function is also the factory reset. Not sure about the 50/500U Models so write down the pictures setting (if you need to) just in case.
Samsung 55KS800 • Pioneer Elite VSX-90TXV • Oppo BDP-103D
Paradigm Studio 10's • Paradigm Studio CC-490 • Sunfire HRS-8