A while back, I wrote about losing non-HDMI audio after updating an AMD graphics card driver. The cause, as it turned out, had nothing to do with the software; it was the monitor that was switched to HDMI audio input instead of analog input.

But more recently, I ran into the opposite problem: no HDMI audio, and the HDMI audio device always busy. This, too, happened after a driver upgrade, but in this case, the software was, in fact, at fault.

The solution, in this case, was to roll back the HDMI audio driver, specifically to the 7721 version.