Waxing Cerebral

My sound stopped after having worked for 6 months. I hadn't run any updates, and even tried booting into previous kernels to check, but that didn't help. Finally I discovered the answer, but not thanks to internet searching. Here are the requirements:

1. If you are running linux
2. If you have Windows on another partition you can dual boot into
3. If sound works ok in Windows
   

and here is the first 2 steps:

1. Check for a hardware mute switch and/or volume control on the machine (especially laptops) - this will affect Windows as well, so if it's currently working there then this won't be the problem
2. Boot into Windows. Unmute the sound. Try linux again

So that was my problem. I had muted sound whilst in Windows, not realising that Windows can hardware-mute the sound card, something that linux doesn't have control over. So when re-booting into linux, it thought it was playing sound fine, but I could hear nada. Hope this helps someone :)

The silver-lining in this exercise in frustration was fixing my VLC performance. I had noticed for a few weeks that music and movies played in VLC would be silent for the first 10s or so. Running VLC in terminal gave complaints about pulseaudio not found.
Solution here for me was to go into the VLC preferences> Output Modules and check the box for advanced options. Change 'Audio Output Module' from default to 'ALSA audio output'.
The alternative option would be to install pulseaudio (sudo aptitude install pulseaudio). It seems pulseaudio is the new default sound server in Ubuntu and provides more advanced sound functionality, particularly when it comes to combining sounds, so this may be the best chouce.