Go here get driver sweeper;
Guru3D - Driver Sweeper
Install it, read how to use it under the help tab. You have to run it as administrator.
Start, Control Panel, Programs, Uninstall a program,
Uninstall your audio drivers. Anything labled Realtek
Do not restart when requested but use Driversweeper to check that everything is uninstalled.
Restart your computer vista will detect your hardware and install drivers. You may have to accept a UAC prompt.
You will not have the Realtek software this is unimportant.
Try your sound.
You may have to set it up by right clicking on the speaker symbol and selecting Playback devices.
Should look like the attached.
I hope this helps
Pooch