Hello, I have a Samsung plasma pn50a650t1f. It has great picture for about a half hour and then the pixels start messing up, it gradually gets worse. The best I can describe it, there are red pixel clouds and it gets bad enough that there are spots that go completely black, like clouds. If turned off for 30 seconds and back on, it makes the TV work right again, like nothings wrong. What's wrong with the tv?