Firstly the latest version of avast is 4.7.827 so rather than chase an issue with an older version I would suggest you download the latest version and save it to your hard disk.
Having done that uninstall the old version and reboot, install the latest version you downloaded and boot.
You could of course do a manual program update, that would save any program settings you have changed/customised, etc.
However, I personally wouldn't update over the top of an existing problem, just in case it was carried forward too. But, trying it wouldn't hurt if it didn't work, just uninstall, reboot and install the latest version you downloaded.