Contact sales @ avast.com (without the spaces) and give them as much information as possible. Date, how you purchased (through Share*it or an avast distributors/resellers), the email that your registration key was sent.
I suggest you have a backup system in place, and save important emails, registrations, etc. and anything else you don't want to lose, emails (also account settings, address book), receipts, data files (.doc, .xls, etc.), Favourites/bookmarks, etc. etc.
