If you're running windows 7, you can also have it automatically detect your service tag by installing a few plug-ins. If it's the internal video card, you can get the drivers off that site.
If it's an ATI/AMD video card, go to AMD.com and hunt down drivers for that model.
If it's an nvidia card, go to nvidia.com, auto-detect your card and install the newest set of drivers.
I am from Dell. The compatible drivers for your Dell Video Card are present on the Drivers and Utilities Disc that was shipped with the computer. However, if you don't have the Drivers disc with you, you can always download and install the drivers from our support site. Please go through the following link for instructions on how to install Drivers: http://support.dell.com/support/topics/global.aspx/supp...
Just select the appropriate links on this page and it will take you to the relevant download pages.
Hope this answers your query. Please do reply if you need any further help.
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