CraigB
8
Are you using the newest release https://forum.avast.com/index.php?topic=176600.0 ? if so then please try a clean install, uninstall Avast first from Programs and Features then run avastclean and follow with reinstalling a fresh copy of the latest release which should be downloaded and saved prior to removing your existing copy.
Also run vendors removal tools for any other AV’s you may have used in the past to remove remnants which could possibly cause conflicts.