Hi,
I've got a similar problem. I thought it was a virus I might have caught during a trip to Thailand, but I can't be sure.
I have Avast Internet Security 5.0.462 (the paid version), running on Win XP SP2.
Everyhting was fine until one day, I noticed the X on the Avast icon. When I open Avast now, in the status window, it says that my system is unsecured. I tried the buttons "repair" (not sure of the English word because I'm using the French version which says "rétablir") and "start the program" ("démarrer le programme"), but nothing happened.
Then following some advice from this forum, I went to Add/Delete programs in Windows, found Avast, clicked on modify/delete and then chose "repair". I got: Error processing packages. Please use full update.
Also, my computer can't connect to Internet (and I've got other computers in the house that do, so the problem is with this computer).
I used to have the free version and switched to the paid one, but the new version worked fine for a while.
Thanks for your help,
Charles