Before replacing the power board, check for cold solder joints on the large square component (not sure if it is a rectifier or voltage regulator, but it gets hot when the TV is on). My Samsung would stop working, no red light and sometimes after sitting for hours it would work again. The heating up/cooling down of this component must have put stress on the solder joints and caused breakage leading to intermittent contact. Reheating/reflowing the solder has fixed the issue for me. Look for rings around the terminals where the solder had broken. Good luck.