Hi there
First of all,I love Avast!
I’ve been using Avast for more than 2 years
But now I use windows 8(64 bit) and when I install Avast,after first restart,i can’t use my PC
I type in my PIN(windows 8) and please wait sign stays unusually long,then black screen…I can’t see start screen,I can’t see desktop…I just launch task manager,open explorer from there and uninstall avast.Then everything is OK
Additional details:
I tried both avast 7 and avast 8,no luck
I don’t have any issues with other antiviruses(My keyboard’s media control keys doesn’t work when I use AVG)
i5,windows8-64bit…can provide any other information
Thanks in advance
Did you try a clean install? Ran aswclear on all previous versions of Avast installed. I’m running Windows 8 64 bit and have no problems.
Yeah,Avast was one of the first apps I installed on a clean windows 8
You said avast was one of the first apps you installed on win8 but in your first reply you also mentioned trying AVG, so have you thoroughly cleaned all remnants of other AV’s before installing avast ?
Many uninstaller tools can be found here http://singularlabs.com/uninstallers/security-software/ if needed, always read the info sections first before running the tools.
I tested some other AV soft after some unsuccessful experience with Avast
If paid version of avast will not cause the same problem,I’m willing to buy
I also have this problem. The temporary solution is unticking the “Monitor system for unauthorized modification” in the settings of Behavior Shield.
You can modify this when you first install Avast or if you restart your computer and get the black screen, press ctrl+alt+del and open the task manager. Click File, run new task and go to your avast folder (C:\Program Files\Avast), open the file “AvastUI.exe” to bring up the main Avast UI. Click security, behavior shield, settings. After that you will see the “Monitor system for unauthorized modification” option, untick it and sign out of your computer and login again.
It will make windows start properly but disable one of the most important function of Behavior Shield at the same time.
I’ve reported this problem to avast feedback page but have yet to receive a reply. 
Thanks YumeHana,your help is much appreciated! 
Please let me know if you’ll get an answer by commenting here,I’ll check this topic daily
And I will give a try to this workaround
Hi, i can confirm the same problem, blank screen with only mouse cursor after installing avast 8 on my acer W700 i3 Windows 8 Pro. Unfortunately initially i did not suspect Avast since i have been using for many years, thus i did a clean install of my system (not refresh) and debug by installing 1 app and rebooting at a time.
I know i should not demand more since i am using only free version, but AV that breaks the system instead of protecting is rather serious. I hope avast can be more careful in future on the update and wish Avast all the best. Thanks! 
Hey everyone avast fans out there check out this post in forzeal.com which will solve avast black screen issue or go to the direct link
here — http://forzeal.com/avast-black-screen-problem 8)
Hello my friends. I have exactly the same problem with black screen in Windows 8 PRO. And I found out what causes it (very likely). The issue was made by a loader/activator for windows 8. But I do not know how to solve this issue without untick “Monitor system for unauthorized modification” option.
hey i hav got an reply from avast feedback go here http://forzeal.com/avast-black-screen-problem/ for detailed explanation u can solve the problem with out unticking the Monitor the system for unauthorized modifications
thank you