I saw a sound card that's just like this, it's an old OEM SoundBlaster Live card (I think). It seems to get recognized by Windows okay, but completely useless after that. There is no mixer, there is no sound, no programs have access to it, etc etc, even though it's a recognized device.
Soltuion = install drivers. The card came with a CD for drivers which seemed to be very specific to her sound card even though it was a soundblaster card. I don't know if you have the same problem, but that fixed this one...