-These Samsung TVs have are common to have bad LCD screens. The common symptom for this is the TVs backlight will turn on then back off for a moment. It will continue this cycle until it is unplugged. Don't order if this is your problem. 

-You can test that both the backlights and power supply circuit is working correctly by unplugging the cable that connects the power supply to the mainboard. If the backlights turn on and stay on, the power supply and backlights are good. Then your problem will be the mainboard or a bad panel.