Hi all,
I encountered problems similar to all of yours (I have a Sony VAIO), and here’s what worked for me:
Check out the Microsoft Support page for an explanation of the problem (specifically with a SigmaTel HD audio device):
After you upgrade to Windows Vista, audio playback no longer works on the computer if the SigmaTel HD audio driver is installed
What you need to do then is go to your specific OEM website to download a new driver for the audio device. You can find links to these OEM websites here (choose based on your computer manufacturer):
Synaptics Products :: OEM Links
Once you get to the OEM website (in my case, Sony), go to the Software & Drivers area and input your computer model. Then follow the directions for downloading and executing the specific update driver for the audio device. Restart your computer, and if you’re as lucky as I was, everything will be back in working order.
Hope this help . . .