Thanks guys - seems very odd. My Chrome and Flash are up to date and maybe I was blaming Avast when I shouldn’t!
However, I’m left with a non working youtube! Symptoms again are - go to youtube and pick any vid. Normal box comes up but with no arrow in the middle. Along the bottom ‘progress’ line on the left it shows ‘paused’. If I move my curser along the line I see individual frames of the vid but no sound. And that’s it! Any ideas anybody?