Display out of position

Hello,
I'm using an NVidia GTX 275 grafics card, Hanns G Hi221 monitor running at 1680x1050, and Windows 7 operating system. Everything was working great until today when I turned on my computer and noticed that the display was shifted down about 1cm, so I could not see a portion of the task bar on the desktop.
I wend into the NVidia control panel and adjusted the screen position up, only to find that although I could see the bottom part of the screen now, there was a black strip over the top part of the desktop. So just to clarify, now the bottom is in the correct position, but there is a 1cm black strip across the top part of my screen. When I run games however, the strip is gone and everything is positioned correctly. Also I tried a print screen, and on viewing it in paint everything was showing correctly with no black strip. Any thoughts on how to fix this problem? Thanks for your help!!!