After updating a new HD - not more - (by Image copy) I had to re-input the registration; no prblm so far.
But Avast doesn’t appear in the system tray any more (option is picked). So I’m a little uncertain if it my cause any problems or doesn’t work any more 100%.
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).