Do you have all the original discs that came with the computer? If so, you'll have to reinstall the drivers for the onboard audio from the appropriate CD. There should also be a manual with instructions on how to do it. You could also go HERE
(links to Dell website for 4550 downloads). From here, download whatever you need and install it on your computer.
Let us know how you fare with this, and we'll go from there!
War produces veterans, wounded both physically and mentally. They have sacrificed for us.....and it is now our job to help these veterans, as they have already helped us in ways we will never know, in ways that we cannot fathom, and in ways that we take granted every day.