I had the same symptoms on the same tv. Samsung sent a tech and they replaced the X-Main. With the rear cover removed, it is the board on the top right hand side. Seemed very easy to do. The tech said the board (x-main) would have cost $120 plus labor.
Tonight I was watching tv and all of a sudden it just shut off on me randomly and the red stand by light started flashing. It wouldn't turn on at all so I unplugged the tv and plugged it back in and it all it does is click a few times like it's trying to turn on and then after 5 seconds or so the clicking stops and the red stand by light just blinks twice pauses and blinks twice over and over again.