Try this (you should have files in C:\Program Files\Realtek\InstallShield,
from the Realtek installation):
First, allow Vista to change your audio driver to the generic High
Definition driver (the one that doesn't work). On your keyboard, press the
Windows key + R. In the Run box, type
msconfig
On the Startup tab of System Configuration, if there are any files from
Realtek Semiconductor, remove the checkmark for those, such as RtHDVCpl.exe
(there may be others). (Apply, OK) and restart. (Tell System Configuration
not to show you it's message or run again when you see that prompt after
re-booting). Note: the appropriate startup item(s) will be re-entered
automatically when the new driver from Realtek is installed.
Then, in Device Manager, double-click the generic High Definition driver,
under "Sound, video and game controllers", and, on the Driver tab, choose
Update Driver. Then choose "Browse my computer for driver software." Under
"Search for driver software in this location", Browse to C:\Program
Files\Realtek\InstallShield. Click OK once you've found that folder, then
click Next...