This really should be in its own topic as it is not for the same version and you version is well out of date.
My recommendation is do a clean install of the latest version as there is little benefit in chasing problems in old versions.
This assumes you are using the avast free version:
- Download the latest version of avast, 7.0.1466
http://files.avast.com/iavs5x/avast_free_antivirus_setup.exe 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 5.x, 6.0.x and 7.0.x).
- 1. Now uninstall avast! (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 6.x if previously installed and then for 7.0, once complete reboot into normal mode.
- 3. install the latest version, reboot.
Edit typo version avast number.