need sound advice

[d14099]

i have xp pro i am using boston acoustic ba7800 speaker system originally a gateway # i have a mad dog sound card, it has been working great for about a year now, but i just lost the sound from the 2 front speakers i can hear it the signal coming from the subwoofer, the 2 rear speakers and the subwoofer work.
i went to the vo;ume control program and from the options drop down i can see advanced controls but i cant highlight it to make the changes i need to make which i believe change from digital to analog
is there a way to fix this
thanks
david