Does the line remain behind where it is if you drag the Taskbar down, or move it to some other place on the screen, eg top, left, right?
If it remains there, then I would have a look at the Desktop image itself, and see if the line is on that.
Mark
It can be viewed here http://img266.imageshack.us/i/windows7line.png/
Btw, click on the pic to zoom in.
Also, when I pull up the taskbar, the line becomes a faint white streak about 2 1/2 inches (the line does not move with the taskbar when pulled up).
Note: THE RED BOX ISN'T THE LINE, IT'S JUST OUTLINING THE ACTUAL HORIZONTAL LINE.

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