I faced the same problem sometime ago and I had to go toDell suport (because myAMT machineis Dell). They told me I had to manually close a circuit on the base board (using a jumper), so they sent me a diagram to illustrate the procedure. Maybe you need to contact the manufacturer of your PC so they can give you specific steps.
Do you have an option to disable AMT in the Bios? If you could get your system back to Factory mode, that would reset the ME password back to "admin". Also, if you can figure out where the system's cmos battery is and take it out for 20 seconds (and then put it all back together again) this would reset the passwordback to "admin" as well.