Samsung HLN617W unresponsive black and white pixels

I have a four year old Samsung DLP Model HLN617W (SiteModel HLN617W1X/XAA) that has generally worked well. I've had the lamp replaced once. Just last night, while watching a VHS tape, the picture changed to black and white. The sound was still audible and not distorted. The picture looked like it was composed of black and white pixels, and the image had frozen. The TV would not turn off using the remote of the side panel on/off button. I had to turn off the power strip. I was hoping the problem was my old DVD/VHS unit. No such luck. Today, viewing cable TV, the same failure occurred after about 15 minutes. The next day, it went for over an hour before the picture changed to frozen black and white again. It seems to be related to the TV getting hot. Has anyone experienced this type of failure? Any idea what the cause and/or fix is?