I have a similar issue and have seen others with the same problem of unrecognised AC'97 after h/w or o/s changes.
I replaced a power supply, had a problem with the USB ports, deleted and reloaded the drivers and then noticed I had no audio. I deleted the realtek drivers assuming they'd be reloaded. They weren't!
I've removed and reloaded a variety of AC'97 drivers in regular and safe mode, disabled & re-enabled AC'97 BIOS etc but all I can load is a 'unimodem half-duplex audio device.
Emachines suggest the on board audio is u/s and since a standalone card in only $20 that's probably what I'll do. I'm just frustrated I can't make it work!
If anyone has the driver, would they email to
sh0@hotmail.com . Thanks