HI my solution would be to go to avast.com and download the free version of avast free and reinstall it. make sure to uninstall avast pro first though.
Uninstall avast! 8 via add/remove? Restart your machine. Download the avast! uninstall utility, but don’t run it. Turn your machine in safe mode and run the avast! uninstall utility. It will ask you to restart. Download and install avast!8 Free version