I have a new HTPC build (it's running Windows 7 Ultimate x64) and it has a ATI Radeon 6450 as graphics card.
When I boot the PC, everything works fine. However, when the TV is turned off and then back on I notice there's no sound anymore. There are lots of other people who have this issue aswell. I've found this workaround however it doesn't seem to work for me.
I have the newest drivers (12.4). Someone said it was fixed in 9.1 but I still have the issue.