I'm very sorry for any inconvenience this may have caused you. The easiest way to see if this is a problem with the TV or with an external source is to turn on the TV's menu. If the line is behind the menu, then contact the external source manufacturer, as it's probably due to the external source. If the line cuts through the menu still, then it'll need servicing. Here's the thread where you can get details on setting that up: http://forums.cnet.com/7723-13973_102-542437/service-issues-click-here-for-help/
I have a Samsung Plasma SP-S4223 and just recently a thin horizontal black line appeared on my tv. The tv was not dropped or moved in any way. It just appeared one day. Does this mean my screen is gone or can it be fixed? And if so, is this a costly fix? My tv is not that old and has not been used very much.