When you use the Recovery Console, after renaming the Administrator account, you are prompted for the password of the account named Administrator?
The text on the Recovery Console logon screen does NOT reflect the new name of the Administrator account.
Simply enter the password of the renamed account.
NOTE: The Recovery Console requires that you logon with the built-in Administrator account. It can tell that your renamed account is the built-in Administrator because it's SID ends with -500.
NOTE: To rename the Administrator account, use the Rename administrator account policy at
\Computer Configuration\Windows Settings\Security Settings\Local Policies\Security Options