Ok... it's a bit chaotic here... I'm listing the problems I have, please help !
When upgrading windows 10 from 7 or 8 :
The existing user profiles are OK. We log with a new user on the windows 10 station and the start menu won't show. Also, the task bar is empty and the search files doesn't work. Basically, only what's on the desktop works.
On any Windows 10 stations :
The keyboard doesn't work. It sounds silly I know, but it's really Avast causing this.
On any Windows 8 to 10 stations :
The upgarde to 8.0.1606 causes blue screens. It depends on the computers, most of the time, it's once a day. On others, it's more.
For each problems, we uninstall, then reinstall. The worst is the keyboard problem. It may come back, or not. On some computers, we uninstalled Avast 4 times. On each and every case, if we don't re-install Avast, every problems are solved...