Here is how I solved this problem. I forced windows to find a solution. Here are the steps I took:
1. Disabled Nvidia high def audio under devices in the control panel.
2. Set windows audio services to manual.
3. Rebooted. The sound device icon s/b red xed indicating a sound problem.
4. RIght click on the icon and select the trouble shoot.
5. Accept the fixes as directed.
6. Test for sound. Reboot if necessary.
Then I noticed that windows had enabled Nvidia high def audio under devices and set windows audio services to automatic. Although I had tried doing all of those things myself, the fix did not take until I forced windows to run the troubleshoot. Also, you should have installed your card drivers with the clean install option as already posted.