Why is it this sort of thing usually happens latish in the evening?
Last night, for the first time since October, I decided to boot GuildWars 2. I rapidly noticed a serious lack of sound. Any sound.
Reboot computer. Restart game. No sound. No sound via speakers or headphones.
Boot Sims 3 - no sound.
In fact, the only sound I can get is via web browser - youtube videos and the like work.
Eventually I remember that I updated Windows a couple of weeks ago. I went checking and the laptop I'm using has its own sound system on top of Windows. And the support assistant for the system says there's an update for that software. Being midnight, I shut the computer and go to bed.
The next morning, get the update and install. Lo and behold, the computer has sound again - speakers or headphones. GuildWars and Sims both have sound too.