sorry i have zero experience with multiple monitors, but i think maybe you can try newer drivers? use driver sweeper program to remove old ones, restart. I am not sure what OS you are running (Vista or 7), so select what you need on this page, http://www.nvidia.com/Download/index.aspx?lang=en-us
and download and run the driver. see if that helps. If the company that built the computer installed the driver, maybe you have an old driver.
what i do is save the new, downloaded driver to the desktop. Remove your old one, restart, and run new driver from desktop. i hope you get it sorted out