I can't tell you any answers, because I don't really know how I got it sorted.
Can only suggest you do a search here for AC97 - some of the threads, where what I used.
I do remember that it was a bit of a swine to get sorted - something to do with my "brookdale" chipset.
I presume that you have tried the obvious ones like checking the sound isn't muted in a mixer - kmix or better still aumix.
then go into the mandrake control centre and look at the hardware - see if it's there. Or into system and look to see if the device is there!
Oh and I will admit, that while I did get it going, I ended up buying a soundblaster live! 5.1 - I just couldn't do the stress bit of setting it back up again when I screwed my system.