I have been looking at this issue for a while.
I am running Windows 10 Pro 64 Bit Version 1703 OS Build 15063.540
I have tried to create a new user tonight, I tried to add my son through microsoft family and the account would simply not login, I switched him to an administrators account and I got in but the account is badly damaged, no startmenu, no background no nothing.
I removed him from my family and decided to create an account manually using
net user /add testuser1 <password> net localgroup Administrators testuser1 /add
both commands executed successfully.
When I log in I am greeted with a totally black background, the taskbar is there but the start menus isn't there and I can't launch anything at all not even cmd.exe from the run box.
I'm not sure why this has happened I have 3 accounts on the machine that work perfectly and my log is not full of errors. I am wondering if the accounts are based on some sort of template that may be corrupt but I am a little beyond my ops knowledge.
This is a dev box albeit a home one and would incur significant effort to reinstall so before I do that does anyone know how to fix this? I can't create new accounts that I can use to log in on. At least interactively.
Also worth a mention is if I create the user as a normal user and not an administrator it simply doesn't leave the login screen but immediately logs them out.
Interestingly all other accounts were created before creators update, Hmm I wonder.