Richard, Did not even get the opportunity to try your remedy, as the sound came back on unexpectedly. I have experienced the same thing on the odd occasion in the past. No sound, then it shows up again.
I also experience the same thing with the battery/power icon. It disappears, then when entering the control panel I am unable to re-install the battery icon at the bottom right hand corner of the screen. Next day when starting up - enter the control panel, and it will then accept the tick in the power box, and the battery icon re-appears.
Thanks, all the same though, and I will make a note of your suggestion for future use.