I have a 42 in samsung plasma tv (PL-42P5HD)..all it's normal, but sometimes when l watcha movie or play games. my tv screen just show a half screen. (up)black and the other part (below)..the movie or the game.[--].so lm turn off and turn on and work fine...?? so what l need to do..isn' a electrical power trouble or what is..pls help if anyone know or got the same problem?? thanks