Failure to log in to windows

Hello. After the update avast asked me to reboot the system. I agreed, clicked “reboot now” and after the reboot Windows started to ask for a password to log in, although no one had ever set such a password and before at this stage of booting the computer just pressed enter and the system booted with an empty password. Therefore, to download and install the utilities and applications recommended in other similar threads of the forum, just not possible, because even to the desktop does not come up, as you understand. Safe mode and everything else that is suggested in the list when I press F8, has been tried.
What to do?