Screen has shadows after memory upgrade.

I have a NVIDIA GeForce2 MX video card. I just upgraded my memory from 256MB to 512MB. Now I have shadows on my screen that weren't there before. I do have an extention video cord on this system. I have seen this on other systems at work that have video extention cords. Is there anyway to get rid of the shadows without having to remove the video extention cord? Thanks in advance.