Try rebooting the machine into "safe mode" (google it).
Then open the "services" control panel (within "Administrative tools"), double-click the "Avast Cleanup Premium" service, and click the "startup type" pop-up list, changing from "Automatic" to "disabled". Then reboot the machine, and you should find it works OK then. Although the Avast Cleanup application will give an error message if you try to run it (as it needs the service running to work).