When hardware goes wrong I tend to uninstall any drivers I’ve tried to install, disable the hardware and reboot.
You will be prompted to install the driver on restart.. just say no.
The AC97 driver doesn’t install automatically.. although I’ve never understood why!Nearly every mother board on the planet with sound, uses AC97 sound. That aside. I would also re-download the AC97 driver for your card to0 make sure it wasn’t corrupted and check that the AC97 you are downloading matches the card.. sorry if I’m telling you how to suck eggs, but this is the most common problem with AC97 driver installations.
If you have used the drivers you are now installing previously are you running your OS at the same Service Pack level etc? Anything changed? Have you reseated the card recently?