I have a RCA D52W20 52' It will turn on fine but

I have a RCA D52W20 52' It will turn on fine but after waching it for about 15 or 20 minutes it will blink to black and come back on for about 5 seconds then do it again then power off compleatly. You can turn it back on after 5 minutes but it will only stay on for a couple minutes then do the same thing again. What do I do? I want to fix it myself because I don't want to pay $300 for a repair man.