intel 915GAV board...hmm.....do u see realtek sound manager in ur taskbar???
if u happen to see it,double click it,click on speaker configuration on top row,nd choose 4CH Speaker...
if u dont happen to see realtek software,then go to run > msconfig, nd have a luk at the entries..see if u can find "SOUNDMAN",make sure is checked,restart nd have a try....
moreover which software ru using to view media files???
i was having the same problem in 6.1,but the software i was using was winamp,nd that seemed to be the culprit in my case,switched to media player 10,nd all speakers r boomin fine!!!!!
keep ur fingers crossed....!!!