The problem may be with your video source options which may not even be a problem at all. With my Vizio and my PS3 in the middle of games and movies it would black out and turn off. I contacted my Vizio rep and he had me simply change an Backlight Option from Auto to Off. Extremely simple and quick, according to him some TVs have a problem re-enabling the display when the backlight changes state. This would simply make your video picture brighter or not.
Just looked again at my TV, and I have this setting only when I select my video source as HDMI, and then view my Video Settings. I don't know how similar or different the LG settings are.
