If you got physical access to your Windows machine or server and forgot your password, simply boot with a WinPE Live disk and replace either
sethc.exe or utilman.exe with cmd.exe

copy c:\windows\system32\cmd.exe c:\windows\system32\sethc.exe

Now reboot and at the password prompt, hit the SHIFT key 5 times to open command prompt

or
copy c:\windows\system32\cmd.exe c:\windows\system32\Utilman.exe
reboot and hit the keys CTRL + U to open the cmd prompt

now type this to set a new password:
net user your_username new_password

or type this to create a new user:
net user your_username new_password /add
and this command to add this new user to the admin group:
net localgroup Administrators your_username /add

Now type in your new password and youre set!
This works on Windows 7, Windows 8.1, Windows 10, Windows Server 2012 R2, Windows Server 2016 and all other Windows and Server editions.