David thanks pal, you know so much more about computers than me, and you are living proof of how experts quickly forget what it's like to be a beginner. Your "simplified" reply was couched in computer terms, that , while easily understood by someone with your expertise, made no sense at all to me. Could I ask you to re-read it as it would appear to you A FEW WEEKS AFTER YOU ACQUIRED YOUR FIRST COMPUTER.
Anyway...at the end of my tether, I uninstalled and then re-installed Avast and, bingo my icon is restored. So simple, so quick.
Thanks pal,
Andy