My 55-inch Philips PUS 8007 Ambilight TV Has a Horizontal Line Across the Screen

I have a 55-inch Philips PUS 8007 Ambilight TV, and I'm having trouble with it. At the top of the screen, there is a straight horizontal line that goes from one corner to the other. This problem started after the second time I used it, and it's making it hard for me to watch TV. As part of my dowry, I bought this TV. I thought it would work perfectly. I'm not sure what I can do to fix this problem. Has anyone else had a problem like this with a Philips TV? I really hope Philips takes care of this quickly and finds a solution. I'm looking for answers and ways to fix my TV so that it works at its best again.