if you don't unplug it... your battery will die. AND... DO NOT hook up a charger while the lanyard is connected. It could kill your MPEM.
Since it started... the MPEM is fine. It sounds like the lanyard post is starting to fail.
If you push the button 5 times... you should get a long and a short beep. That's telling you that it's in advanced mode. From there, you put on the lanyard, and press the button one more time. The beeps that follow give you the condition of the system.