Look through the disks that came with your Dell for one with "drivers" on the label. It may be labeled "Resource" but it will say somewhere on the label that it contains drivers.
Put that CD in the CD drive and when it opens up, read the instructions on how to use it.
Install the "System" drivers first, then the display (video) drivers and the sound (audio) drivers.
If you don't have or can't find that CD, go to
this Dell support page, enter the information about your computer and eventually you'll get to a page with links to download the necessary drivers.