Use a system inventory program to see what video card you have. If your
video is integrated (on the motherboard), also look at the motherboard
type. This will tell you the correct video driver to download from Dell. If
you aren't getting the right resolution, you haven't installed the correct
drivers.
http://www.belarc.com/free_download.html - Belarc Advisor
http://www.gtopala.com/ - System Information for Windows
Malke