Try downloading RejZor’s avast! External Control program and use the - Perform Forced Uninstall. Reboot and try the install again.

Have you got any other AV installed, let us know more about your system.

Please Help us to Help you - User’s FAQ - we need more information to be able to help fully. A visit to the - thread will give you a lot of useful advice and an idea of the information needed to Help you fully.

HTH David