kf-50we610 turns off then back on

[guidoia]

I bought a used sony kf-50we610. When I turn the TV on it works great for about 45 seconds then the lamp and the sound turn off. The led in front still stays green. after about 15 seconds the lamp and sound turn back on. 30 seconds later it will go off again. This keeps repeating and doesn't stop. The LED never goes out or changes from green. The two fans in the back seem to be running fine. Any help would be appreciated. Thanks