Help, please: Can not adjust picture position

I'd take it back. There are too many good TVs out there for you to have to put up with a bad one.

First if you are seeing what seems like black and white pixels at the VERY top of the screen, only a few rows of pixels wide, that is "normal" in that it's the Closed Captioning info that some stations broadcast, and would get lost by older TV's that have overscanning built in. Second the issue with the position option not being able to be viewed, that option is only available with the certain view modes and resolutions. I believe it's really only available when using the "Dot by Dot" mode.

Lutch is correct. The line is broadcast info which is always present, tho normally it is hidden behind the bazel of the tv. The only time you'll see it is if you have the tv set to one to one pixel mapping, or dot to dot mode, or just scan, or whatever your tv calls it when you turn off overscan.

To remove the line be sure overscan is enabled in your tv's settings, and it will go away. Many people turn overscan OFF for computer use, but otherwise, leave overscan on so you don't see the broadcast info which is annoying you.