If you forgot the administrator password on Windows server, this steps may help you.
This can be implemented on Windows 2012 R2 and later.
Boot the server from the Windows Server 2016 Installation DVD. When the Setup screen appears, press SHIFT + F10 keys to open Command Prompt.
At the Command Prompt, go to drive where windows was installed, and run the following steps:
d: (depending on the C:\ system is located when it's being booted). cd Windows\System32 ren Utilman.exe Utilman.exe.original copy cmd.exe Utilman.exe shutdown -r -t 0
Once you have in normal logon screen, press Windows Key + U or click the Ease of Access button, Command Prompt will pop up and type:
net user Administrator [email protected]
Login with the new password. Once you’re able to login, browse to the directory
C:\Windows\System32, delete Utilman.exe and rename Utilman.exe.original back to Utilman.exe.