A clean reinstall, including the use of the avast uninstall utility:
- Download the latest version of avast, 8.0.1483 and save it to your HDD, somewhere you can find it again (if you didn't save your last download). Use that when you reinstall.
- Download the avast! Uninstall Utility, aswClear.exe
find it here and save it to your HDD (it has uninstall tools for all versions).
- 1. Now uninstall avast! (using add remove programs, if you can't do that, as appears to be the case then start from the next step), reboot.
- 2. run the avast! Uninstall Utility, it will request it be run from safe mode (and will handle the boot into safe mode), first for 7.x if previously installed and then for 8.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.