It sounds like an internal failure. I'd check my warranty and if close, extend my warranty then call it in. There are no user serviceable parts for this failure.
Recently I had a very short line of pixels appear on this TV (about 1 inch long). The line has grown over the last few weeks and is now about 18 inches. It is very prominent when the picture on the TV is lighter colors. When the scene changes to darker colors the line almost disappears ... like these pixels still are capable of some darker colors but not medium to light colors. How can I trouble shoot to narrow down the problem?