Then boot into safe mode where avast doesn't run by default (the purpose of safe mode) and as such neither does the self-defence module.
You should be able to reinstall through add remove programs even in normal mode without having to disable the self-defence module.
It would probably be best to do a clean reinstall:
Download the latest version of avast, AIS 5.0.507 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, aswClear5.exe find it here
and save it to your HDD (it has uninstall tools for both 4.8 and 5.0).
- 1. Now uninstall (using add remove programs, if you can't do that start from the next step), reboot.
- 2. run the avast! Uninstall Utility from safe mode, first for 4.8 if previously installed and then for 5.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.