From the list of topics in the avast 4 Home/Pro Forum, at the top of the page you should see a New Topic button, see image.

Since the repair didn’t work, try, uninstall, reboot, install, reboot.
It would probably be best to download the latest version of avast http://www.avast.com/eng/programs.html and save it to your HDD, somewhere you can find it again. Use that when you reinstall.