Martin is having issues creating a new user account on a used computer. Leo says to go into the account settings and look under "access work/school." There's likely a setting in there that requires a login to the domain. Leo says he should be able to remove it. He should disconnect from the server and remove that option. Then reboot. It should work.
Since it's a Windows 10 computer, Leo recommends just starting over. He should download the Microsoft Media Creation tool to create a USB install of Windows 10, then reboot to the USB key, format the hard drive, and reinstall Windows 10.