I had this problem for like a month, finally found the right driver and installed it the following way:
1. Download the audio driver file from here: http://fileme.us/file/0Y1B61
2. Extract it anywhere on your computer.
3. Right-Click on My Computer -> Manage -> Device Manager -> Right-Click on missing audio driver which has a [b]warning sign (!)[/b] on it -> Update Driver
4. Installation Wizard will appear, check "install from a list or specific location" -> NEXT -> Check "include this location on the search" and browse to the [b]extracted[/b] driver location -> Next to install & finish installation :)