If you are experiencing any problems with your computer, for example if your operating system has been corrupted by some other 3rd party software, which prevents avast! 7.x from being correctly uninstalled via Control panel, you can uninstall it using the avast! Uninstall Utility while running Windows in 'Safe Mode':
Firstly download the avast! Uninstall Utility from the avast! website:
http://www.avast.com/uninstall-utility...and save it to your computer, in a location where you will easily be able to locate it. For example save the downloaded file aswclear.exe on your Windows Desktop if you're logged in as Administrator.
Reboot your computer and start Windows in 'Safe mode' according to the instructions on the Microsoft website:
to enter Safe Mode in Windows 8 press shift f8
With Windows running in 'Safe Mode' browse your computer to locate the downloaded file aswclear.exe (depending on your system preferences, the file extension may be hidden). Once you have located it, on your Windows Desktop for example, double-click on it to execute the avast! Uninstall Utility.
On the avast! Uninstall Utility screen select 'avast! 7 Free/Pro/Internet Security' from the drop-down menu as the product to uninstall, if it wasn't already selected automatically.
Then enter the path to the folder where avast! 7.x is installed, if it wasn't detected automatically, or you can click on the button marked '...' on the right,
...and locate the installation folder by browsing via the navigation dialog.
Then click on 'Uninstall' to proceed with the uninstallation of avast! 7.x.
You will be asked to confirm that you want to delete all files in the folder where avast! 7.x is installed. Make sure that entered path is correct and click 'Yes'.
When the uninstallation is complete you will see the message 'Program was successfully removed' in the Uninstall progress status log. Then click on the exit button 'X' (cross) in the top right corner of the window to close the avast! Uninstall Utility.
You will then be asked whether your computer should be restarted. Click to 'Yes' to reboot your computer immediately, or click 'No' if you wish to restart the computer later manually.
then left for a new installation