Picture & sound go on & off every sec, red light blinks 5 times

I have a Sony Wega rear projection 55 inch LCD HDTV. The TV turns on and there is picture and sound for about 30 seconds, then the screen goes blank (no picture or sound) and then comes back on about 30 seconds later, then repeats over and over. The green power light stays on the entire time (even when no sound or picture). If I power off the TV during the period where the screen is blank and no sound and then power it back on, there is a red blinking light where the power light is. It blinks 5 times, pauses, and then repeats. I am then able to turn the TV back on, but the same thing recurs: picture and sound for 30 seconds, then I lose both for 30 seconds, then they come back, etc.