57uwx20B no picture only sound

i was watching a movie with my son and the screen went black with audio. there were no other symptoms just all of a sudden no picture. i turned off the set and let it sit for several minutes, then i turned it on and there was picture again. but soon the picture went to black again with audio. seems like a relay to me or some other part getting hot and failing. this just happened so i have not had the time to open up the set yet. any advice would be greatly appreciated.