It appears as though the video driver isn't loaded ... go to
http://support.dell.com/support/downloads/driverslist.aspx?c=us&l=en&s=gen&ServiceTag=&SystemID=DIM_CEL_3000&os=WW1&osl=en&catid=&impid= and choose video from the list and find your driver and install it... unless of course, you added a different video card, then you'll need to install the driver for that particular card