Hi,
Try using Recovery Manager to reinstall your original IDT HD Audio Driver - the procedure for using recovery manager to reinstall Software and Drivers is detailed in the document on the link below.
Recovery Manager - Windows Vista
After the reinstallation has completed, shutdown the notebook. Unplug the AC Adapter and then remove the battery. Hold down the Power button for 30 seconds. Re-insert the battery and plug in the AC Adapter.
Tap away at the esc key as you start the notebook to launch the Start-up Menu and then select f10 to enter the bios menu. Press f5 to load the defaults ( this is sometimes f9, but the menu at the bottom will show the correct key ), use the arrow keys to select 'Yes' and hit enter. Press f10 to save the setting and again use the arrow keys to select 'Yes' and hit enter.
Let windows fully load for a couple of minutes and then check if your audio is working.
Regards,
DP-K