I've been having the same problem for a couple months. I recently upgraded to Windows 8.1 (from Win7, did a proper hdd wipe) and the problem popped up again shortly after the installation.
Basically Avast won't turn on. I see this screen:
when I click 'Resolve All', the window freezes (goes into Not Responding mode) for about 60 seconds and then I get this other window:
I click no but then it goes back to the first screen, Avast is still off. I still get periodic notifications of 'Avast! Virus database has been updated' but the thing still appears as off. I'm worried I might have a virus that's doing this, maybe one of the programs I use is doing it and that's why the problem persisted through a Windows reinstall.
I tried going into safe mode and doing a full scan. I also uninstalled Avast using the official uninstall utility in safe mode and then reinstalled it. It worked fine until the next restart, when it started misbehaving again.
Help. ;-;