|Well, as post #2 suggested, by the looks of things your PC is lacking audio drivers.|
There are 2 simple ways you can go about this
If your PC is a manufacturer made one (AKA Dell/ACER/Toshiba...ect) then it is likely that they distributed drivers on their website's or supplied you with a driver CD.
Installing the drivers from those sources should be pretty straightforward
If you cannot find the drivers CD for your computer, and cannot find the drivers on the web another way is to use a "Driver search tool".
Driverguide have a tool avalible (dont know how well it works, only used it twice) that searches for drivers, and could possibly find one for you.