Fresh install but with any previous antivirus? OEM?
It’s not a good idea to downgrade… Anyway, I suggest an installation from the scratch:

  1. Uninstall avast from Control Panel first.
  2. Boot.
  3. Use Avast Uninstall for complete uninstallation.
  4. Boot.
  5. Stay off-line (not connected to Internet)
  6. Install again the old version: http://filehippo.com/download_avast_antivirus/
  7. Boot.
  8. Register avast (insert the registration key).
  9. Uncheck the programs updates (set to manual).
  10. Only then connect to Internet (go on-line).
  11. Check and post the results.