Windows Server 12 R after DNS set up

[Silicon Waffle]

After I installed a fresh windows server 2012R, I could log in with administrator account, e.g MYWIN\Administrator (MYWIN is my computer name). Then I created a DNS/forest e.g ABC.com , I then could log in with ABC\Administrator.
For some reason I now sign out and would want to log in with MYWIN\Administrator, but the system says that my password is incorrect (I do enter "MYWIN\Administrator" in username textbox).

 

[Routaran]

Hey Silicon,
By default, as soon as a system is defined as a Domain Controller (DC), you are no longer allowed to log into it locally. Local windows user accounts are stored within the SAM database. When a computer is promoted to a DC, this is replaced with a domain database. So when you provide your local admin credentials, there's nothing for it to check against.

This is normal behaviour for a DC. You must always login with authorised domain credentials.

Cheers