I use Windows 8 Pro x64 with avast! 8 Premier and another pc Windows 8 pro x32 with avast! Free anitivirus.
After installing avast! 2 problem happened:
1. After login "blank screen" happened! and
2. "Change PC settings" option not start!
I solved those problems by adding 2 file in Behavior Shield > Trusted Process. The file 2 are:
1. C:\Windows\explorer.exe [solve "blank screen" problem]
2. CWindows\ImmersiveControlPanel\SystemSettings.exe [Solve "Change PC settings" running problem]
Those problem also solved by unchecking "Monitor the system for unauthorized modifications" in Behavior Shield settings.
FOR PEOPLE WHO CAN'T ACCESS TASK MANAGER(Crash) or SAFE MODE, I HAVE FOUND ANOTHER METHOD..
After login, Press Ctrl+Alt+Del then, click on the Power button. It'll show some error, click OK.
Then, there will be an Error Report. Click on More Details, Scroll down & click on the last Hyperlink (Blue, underlined test). This will open text report in Wordpad.
Click File -> Open. Select All Documents from the dropdown menu at the right-bottom of the window.
Browse to "C:\Program Files\AVAST Software\Avast" & look for AvastUI, Right-click on it & Run as Administrator..
Now you can add the explorer.exe & SystemSettings.exe to Behavioral Shield exceptions as mentioned everywhere.. Restart...
Enjoy!!