I posted a response to this issue today in reponse to Jasoo who posted about the soft touch buttons jamming. I had same issue.
Its likely the circuit board behind behind the invisible buttons.
When it happens try tapping gently on the area behind the bezel where those buttons are and if it generates similar symptoms of turning tv on and off then you can be sure your problem is the same as the one I had.
Help! This is unbelievable. I just bought this Samsung 50 inch plasma no more than 5 months ago and after about 25-30 mins of TV watching, my TV suddenly turns itself off, makes about 3 or 4 rapid "clicking" sounds (like on/off very quickly) and then turns itself on again. Once it's done it the first time, it then does it every 2 to 3 mins, non stop! The only thing I can do is shut the TV for about 15 mins before it starts doing it again after 25 mins. It seems to especially happen when I watch sports.
Can someone please help? Your help would be greatly appreciated. thank you.