Your computer is a HP Media Center 864n, take a look at this from HP on how to solve sound problems, it may be disabled in the BIOS, all the instructions are shown
http://h10025.www1.hp.com/ewfrf/wc/d...dlc=en&lang=en
This is your AC'97 sound driver from HP, it is a different version than the one from Realtekhttp://h10061.www1.hp.com/ccsearch/search?pname=HP+Media+Center+864n+Desktop+PC&opnam e=HP+Media+Center+864n+Desktop+PC&qry=audio+driver &submit.x=4&submit.y=2&method=prodFinder&ctry=uk&l ang=en&dlc=en&sni=306499&search=0
Hope this helps
