Hi WhisperSister. Welcome to avast! Forums.

Which avast!; Pro, IS, Premier ?

Ask avast! to resend your license: http://www.avast.com/en-us/resend-license-paid.php

Repair avast!

With XP

Start > Control panel > Add & Remove programs > select avast! and click " Change/Remove ". Look for " Repair " and click it.

With Vista or win7

Start > Control Panel > Programs > Programs & Features > uninstall a program > select avast! and click " Uninstall/Change ". Look for " Repair "

Reboot when finished.

and then try the license avastlic file that was sent to you. Use one of these 2 methods:
http://www.avast.com/en-us/faq.php?article=AVKB7#articleContent