Hi George48,
Multiple ways of tackling this problem.
Simplest way is to find the new Avast orange ball lower right corner in the 'system tray' if XP, same location if Vista or Win 7. Move the mouse down to the icon and right-click. Pop-up will show, and click 'Open Avast User Interface'.
Another way is to click Start if in XP or Vista, and select Avast! from the Program list.
By the way, the orange icon below will rotate when scanning files, and the name of that file is avastUI.exe. Just so you know.