Solution: If you have black screen and you cannot open Task Manager and the settings you change in safemode aren't working, do the following.
1. Boot up
2. Log in
3. After log in press the Windows Key and D at the same time repeatedly.
4. You SHOULD be at the desktop with no black screen, you can now change the settings
To fix black screen after this follow the instructions below provided by forzeal.com/avast-black-screen-problem/
feedback from avast : Windows 8 black screen problem
security >Behavior Shield > Settings. and click on Trusted Processes
Add the following 2 files by browsing them to this paths C:\Windows\explorer.exe and C:\Windows\ImmersiveControlPanel\SystemSettings.exe
this should solve your black screen problem …..
You can even follow below procedure if the above procedure does not work…..
How to resolve Avast Black Screen Problem in windows 8
Start your computer and log in to your windows 8 OS
After you login with your password or a direct login with out password as usually you will get a black screen if you have an installed avast anti-virus
press ctrl+alt+del and choose task manager , you can also do it by pressing ctrl+shift+Esc .
Go to startup tab in Task manager and right-click your avast! Antivirus there and choose Open file location.
A window will open and click on AvastUI this will open avast user interface .
Now go to security >Behavior Shield > Settings.
Uncheck the ” Monitor the system for unauthorized modifications ” box .