How to restore a user without admin. right?

Question

System administration

Good night, I messed up with the best of intentions - I ask for help.
I decided that my mother would not install viruses, make 2 accounts in Windows 10 - I activated the Administrator and separately created her account for her (that is, there are 2 entries in the system Administrator and Mom).
After setting up the accounts, I tried to hide the Administrator from the login window using the instructions found on the Internet:

Create in HKEY_LOCAL_MACHINE\ SOFTWARE\ Microsoft\Windows NT\ CurrentVersion\ Winlogon\SpecialAccounts\UserList DWORD Administrator:0

This operation was successfully done by me and it disappeared from the login screen. But as it turned out, not only from there. Now the system does not see the Administrator at all. When you try to run something from it - there is no account in the pop-up window and there is only a "no" button. Accordingly, I can not do anything on behalf of the administrator.
What I have tried:

• CTRL + ALT + DEL x2 - Nothing happens;
  
• Run cmd as admin from runas console /u:Administrator cmd - writes wrong password (and in all places where I tried to start Admin by force);
  
• I tried to edit the registry through the installation flash drive with Windows. I loaded the hive, but for some reason the created parameter is missing in the loaded file;
  

How can I remove this entry from the registry and return the Administrator?
Windows 10 1903

Answer 1

Here the fastest solution is to boot from the Live CD and edit the registry.
Here , for example.

Answer 2

How can I remove this entry from the registry and return the Administrator?

Roll back to the desired restore point.

Answer 3

Enter in safe mode.

Answer 4

Download Hiren's BootCD
Boot from it (there is an image for a flash drive)
Select junk to edit Windows passwords
Restore admin or create a user with admin rights
NEVER do something you don't understand again. For mom, it was enough to change the admin password.