I have the same problem and it appears when infected files come in I am not getting the notification I used to get. Downloaded and reinstalled yesterday and it ran OK for 1 day then went back to no icon showing.
Reading the previous post, I looked for ASHdisp in Taskmanager but it was not running, went into the progam file and started it then the icons appeared.
Ashdisp.exe is listed as a start up program in MSconfig so don't understand why it is not starting when pc starts.
I have tried the repair option suggested with no difference.
and the show tray icon is set to 1
Any help appreciated