This can occur if the video driver has not been installed after installing Windows.
You can download the device drivers from Dell WEB site,the support download page. Make sure you select your model desktop or laptop,better still, type in the Service Tag number, it is printed on the label on thebottom of the laptop and on the back or sides of a desktop. (If the Service Taglabel is missing then go into the BIOS setting and on one of the BIOS pages,the Service Tag number will be displayed). This will open the page where thespecific drivers for your model computer are located. Also make sure you selectthe Windows of the drivers for your Windows operating system. Click on thislink to download the drivers: - http://support.dell.com/support/downloads/index.aspx?c=us&l=en&s=gen