But really would like the ICON back please!!!
Do you have any other antivirus installed in your system?
Did you have in the past?
Which one?
Can you try to repair your installation?
Go to Control Panel > Add/Remove programs > avast! antivirus > Remove
Then choose Repair function in the popup window (Repair).
If this does not help, can you uninstall / boot / install / boot again?
You can add that registry key manually but I think the steps I posted before should solve your problem.
Last one, can you check if you have the value ShowTaskbarIcon=1 on the [AAVM] section of the avast4.ini file? See 'Settings' on my signature for more info...