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 Management Engine and Intel® Active Management Technology (Intel® AMT). You will need to re-provision the client after doing this.
Depending on the vendor and BIOS version you may need to re-enable Intel® AMT in the Management Engine as well as management features like SOL and IDE-R.
This applies to: