I just updated the AMD Catalyst driver set to the latest on my desktop computer. During the update, suddenly the sound vanished (I was actually listening to something on my computer while the update took place.)

I found out that I was able to get sound through HDMI. But the on-motherboard audio was gone, even though all drivers seemed to be installed correctly and working correctly.

I tried uninstalling and reinstalling drivers. I also tried downgrading the ATI HDMI audio driver with the expectation the audio functionality would be restored. None of these worked.

Eventually I found out that during the update process, my monitor actually switched from PC audio to HDMI audio. So the PC was emitting audio over the analog speaker output all along just fine... it was my monitor that did not pick it up.

Lesson learned. As to why I had to waste an hour of my life to learn this lesson, that's something I would plan to ask the powers that be when the time came, if only I believed in an afterlife...