I recently purchased a Dell OptiPlex 740 with Windows Vista loaded. Out of the box the sound did not work. Dell support was not able to resolve the issue on the initial contact - chat/remote control. The PC came with SigmaTel HD Audio integated ont eh motherboard. After searching for a solution on the Internet, I found that many people had the same issue with Dell and even some Gateway machines. Some were able to resolve the issue by reinstalling older Windows XPO drivers, for other this did not work.

I was able to resolve the issue by removing all SigmaTel drivers fromt he system and letting Widnows Vista redetect the soundcard and install native Vista audio drivers.

The first thing to do in uninstall any Audio Driver packages which are listed in the Control Panel in  ”Add/Remove Programs.” Next follow these steps:

  1. Open “Device Manager”.
  2. Uninstall the device including the driver files.
  3. When Vista tries to redetect and install the audio drivers, disable the device.
  4. Open the “Properties” and then goto the ”Drivers” on the Audio Device.
  5. Locate and take a note of all the drivers files and paths refering to “SigmaTel” (or another non-Microsoft device).There are about five of them.
  6. Goto Windows/System and deleted all SigmaTel driver files (or other non-Microsoft drivers) you noted in step 5.*
  7. Goto Windows/System32 and deleted all SigmaTel driver files (or other non-Microsoft drivers) you noted in step 5. Likely there is only one file if SigmaTel.*
  8. Deleted the Audio Device again in “Device Manager”, then let Windows Vista redetect the device. It should now install it’s own Microsoft Audio Drivers and work. 

* To delete all of these driver files you may need to stop the “Windows Audio” service and restart it after the file deletion is complete.