We have a Windows Vista laptop. On Monday we hooked it up to external speakers, as we always do, and they worked fine. On Tuesday, we did the same but then the speakers did not work. Weirdly, the laptop internal speaker does work. Nothing was changed between Monday and Tuesday. What happened and, more importantly, how can it be fixed?
BTW we tested with other speakers (and cable) and that didn't help. So it seems like a laptop issue.
If I unplug my speakers during playback, the laptop speakers always work!
Also, I've tried the obvious.
Update: We've found out that it also affects sound via USB! So it is definitely not a hardware issue!
Update 2: After the comments below, I tried reinstalling the drivers. This has not helped.
Solved: Details below in my answer. Bounty therefore instead given to vcsjones whose answer tells us how to prevent this happening. (This is an ASUS laptop with Realtek sound driver.)