If the system has built-in Sound Card,
go to run
type dxdiag and Press enter
Check the System Model
and then google driver for the same system model.
Or go to dell website to search directly there.
If you have any Sound card installed on your system, then you will have to find the driver for that specific Sound card.http://www.asknetinfo.com/intel-dg31pr-realtek-audio-driver-installation.html