Media PC lost all sound suddenly

Hope someone can help with this: have a media PC outputting to a TV through HDMI, both sound and picture. Worked fine up until yesterday, was ok in afternoon, turned on in evening and no sound, picture is fine still. Don't know if anything was updated when it turned on as it wasn't me that booted it up.

In the Playback tab of the Sound panel I have the TV listed, going through AMD High Definition Audio, which is the built in graphics chip. There is no activity in the output bar shown there on the right when things are playing. If I try and do any Test of sounds it instantly says Failed to Play Test Tone. Same happens if I try a Test on the Realtek Digital Output which is the onboard sound, but then nothing is plugged in to that so I don't know if that's as it should be.

Device manager says everything working ok. Any suggestions?

EDIT: if I try the Windows troubleshooter it says "Plug in the Speaker, Headset or Headphone. The Device does not appear to be plugged in."

Tried reinstalling sound drivers with no effect, but did a system roll back and that fixed it. No idea which update was responsible so will probably happen again mind...