It'll be a crook board needing replacement. Take it to a Tv repairer near you, there would be a few around. If its not a simple board swap you could be offered another Plasma Tv as replacement.
Plasma's were the best in image quality, its a shame these TVs weren't given the chance to improve in aspects deterring people then the market wouldn't have been left with these inferior gimmick TVs known as LCDs.