I'm afraid that doesn't sound good.
I'm guessing this line is there regardless of which input you select or what screen format you select, correct?
And this line never moves from one part of the screen to another, it's always in the exact same position, correct?
I wish I had better news for you, but if that line shows up in exactly the same place every time on all inputs and formats, the problem is the actual panel (the screen) itself.
Unless this is under warranty, this is going to be a major expense to fix, and is precisely why I urge anyone who buys a current technology HDTV to get an extended warranty. All of these TV's, regardless of whether it's plasma, LCD, or rear projection, have large and expensive assemblies that cannot be fixed, and must be replaced.
Definitely get an estimate from a tech, but be prepared for a real shocker.
Let me know if there's anything else I can do for you, and thanks for using JustAnswer!