Boot from Windows 10 Media

Choose the option to repair windows

Choose the command prompt option

In the C:\windows\system32 folder:

1. Optionally backup sethc.exe ( ren sethc.exe *.bak )

2. Copy cmd.exe sethc.exe

Reboot windows normally

At password prompt, hit left shift key a few times and you should get a command prompt.

Enter net user username password    (These can be found in c:\users)

Enter the same password at the prompt.