This is your best course, right here on the support forums.
Though this topic should go in the Avast Free/Pro/Premier forum - https://forum.avast.com/index.php?board=2.0.
First try these options and if not resolved start a new topic on the forum mentioned above.
Try a repair of avast as mentioned.
Resend avast License http://www.avast.com/resend-license-paid.php, you will need to enter the email that you used when purchasing the license, e.g. the one that the original email with the link was sent.
