Unfortunately, I'm not sure why that would be happening. Assuming that there wasn't any impact on the panel itself, it may be an issue with the panel or the electronics. Without actually inspecting the unit, it would be difficult to determine.
Just yesterday I noticed dead pixels on my Samsung LCD TV. Some in spots. Some in streaks. Worked just fine yesterday. What's the problem? What's the fix? Anything I can do to check it out before I have to bring it in for repair?