You will need the help of a Windows 10 setup/installation disc.
After you will boot from the setup/installation disc you can replace Utility Manager (Easy of access)
When you will have on the screen the Windows setup screen you need to simultaneously press SHIFT + F10 to access Command prompt window.
Here will ne to replace the utilman.exe with cmd.exe using following commands:
move f:windowssystem32utilman.exe f:windowssystem32utilman.exe.bak
copy f:windowssystem32cmd.exe f:windowssystem32utilman.exe
Where f: is the letter of you USB drive or CD.
After this operation you will need to restart the computer. When you are in the login screen you will press on the button Easy of access and in that moment a Command prompt window will appear.
In this window you will need to type this command net user administrator /active:yes
You have from 5-10 second to enter this command than this window will be closed automatically and this option is not available until you will do again the operation from the beginning.