Horizontal Black Line on Plasma Screen. On my Panasonic TH50PX77U, there is a horizontal black

Question

On my Panasonic TH50PX77U, there is a horizontal black line through the middle of the screen. It shows up on every channel and input. If anyone could please tell me what the problem is, I would really appreciate it. Thanks in advance. Samsung LNT4661F vertical line growing over time down screen, another is starting. I can see the line when the TV is off, too. It just appeared one day, and has been slowly getting longer. I only have a few weeks left on my warranty. Repair person said it was external damage and our fault. I don't think that was the case. HELP, PLEASE!