A television picture is made up of hundreds (often thousands) of horizontal lines, which produce the full picture. The more lines available on the screen, the better the overall resolution and picture quality. However, if you are seeing odd lines or discoloration in the upper horizontal lines on your television screen, it is important you troubleshoot the situation as quickly as possible.
Check the programming information (or the DVD packaging). If the show or movie is "Widescreen" you are going to see a black line at the top and bottom of the picture. This is due to the formatting of the content; there isn't anything you can do to eliminate the lines from view.
Turn off the television and leave it off for a few minutes. It is possible the TV did not turn on correctly. Power the system back up and the horizontal lines are now gone.
Look over the cable connections running from the TV to the outside video source. If the cable is not inserted completely into both devices, the video signal is going to become distorted, which could result in incorrect horizontal lines across the top of the screen.
Perform a factory reset on the television. This changes all the settings back to the original functions that the factory programmed in. The exact reset method is going to vary, depending on the make and model of your television, but the method is listed in the TV's User's Manual (which you might find online at the TV's manufacturing website, if you don't have the manual currently at hand).