Lets see if someone more knowledgable posts a suggestion but clearly sounds like Avast is in some sort of boot loop.
If no one suggests anything then I would try…

  1. Within Windows Program Installs do a Repair on Avast
  2. You could go into Avast and schedule another boot scan and this time let it complete.
  3. Do a clean uninstall and re-install of Avast: http://forum.avast.com/index.php?topic=143284.0

However, the above are at best “guesses” from me…I’d wait for a more expert person to post.
Also, do you have System Restore points set that perhaps are prior to this first boot time scan ?