What I would do:
Go to Device Manager (Start/Run...type devmgmt.msc and hit Enter) and ensure that there is no sound device listed under Sound, Video and Game Controllers. If there is a device listed as AC97 or Sigmatel anything, uninstall it
. If there is any Sigmatel program listed in Add/Remove Programs, I would also uninstall it.
Run chkdsk /r on the system partition.
After the system reboots from successful conclusion of chkdsk /r command...I would double-click the downloaded driver (which should install the files automatically). I would check the Dell instructions for installing to be sure.