How to do an uninstall / clean install of Avast:
1. Save a copy of Avast and save it to your HDD:
http://www.avast.com/download-software – all versions
2. Download the Avast Uninstall Utility
http://files.avast.com/files/eng/aswclear6.exe and save it to your HDD.
3. Disconnect from the Internet at this time.
4. Go to Control Panel and uninstall Avast through Add/Remove Programs if possible and reboot.
5. If Step 4 fails, boot into
Safe Mode (hit F8 repeatedly) and run the Avast Uninstall Tool.
Uninstall ALL prior versions and products of Avast you had on this machine at this time.
6.
Reboot.
7. Install the newest version of Avast and
reboot.
8. Get Internet access and register your copy or add the license key for Free, Pro, or AIS.
9. Update the Avast definitions.
Let us know if you have any questions. Thank you.