All I get on my TV is a narrow horiz. Line. Plus audio.

Is the line very bright? Where is the line.. How old is the TV? TVs, older ones at least, rely on a splitter of sorts to project the image onto the screen. Sometimes that splitter is damaged and only projects the image in one straight line. I would taker it to a TV repair shop, but get an estimate first and ask if it worth repairing.