You need to unplug and pull the CMOS/RTC battery from the system and wait at least five minutes before replacing it. This will reset the computer back to a factory new state allowing you to use the default password to access the Mangement Engine and Intel® AMT. You will need to re-provision the client after doing this.
Depending on the vendor and BIOS version you may need to renable Intel AMT in the Management Engine as well as management features like SOL and IDE-R
This applies to: