It was likely due to stupidity on my part, but recently I’ve been experiencing a mysterious sound problem with my Ubuntu install (Hoary Hedgehog). For some reason I had absolutely no sound output whatsoever on a machine where I’d been successfully using Totem and the Music Player (Rhythmbox). I tried all the tips I could find on the web (including killing esd: the esound daemon), but nothing worked.
At one point I even managed to lose my entire desktop, i.e. when I booted up there was no pretty login screen only the command line. I’m not entirely sure how I did that, but I think it must have been something I did in Synaptic. That freaked me out more than a little bit, but fortunately I thought to run apt-get install ubuntu-desktop which installed a lot of stuff I didn’t recall removing. After that I was able to login into Gnome, but I still didn’t have any sound.
Yesterday, I decided to take another stab at it. I started with the Volume Control window. I already had the main playback volume at the maximum level (it was the first thing I checked when my sound stopped working). But, this time I decided to fiddle with the other sliders to see if anything happened. I launched an MP3 in Totem, and started fiddling with sliders. The first slider I tried was PCM on the capture tab and suddenly I had sound. I still don’t quite understand the relationship there, but I’ve got sound again so I’m not complaining too loud.