Wiring Up a Li-Ion Battery (Band 2)
Typically what happens with a battery with protection when overdischarged is that the cell gets disconnected from external terminals, to prevent deeper discharge. Unfortunatley every cell has certain self-discharge, so the cell continues to drop its voltage, and the protection circuit keeps engaging. So the battery measures zero volts externally. However, the protection circuit usually allow the charge in.

You should try to apply maybe 50-100mA of current to P+ and P- terminals, and wait 10-15 minutes. You can use a 5V source and a 50-100 Ohms resistor in series. If the cell is not completely dead, it should slowly charge above 2.5-3V. Then the protection circuit will disengage, and you can try to charge the battery using normal Li-Ion charger.  However, the battery capacity can be severely diminished, down to zero. The effect depends on how long the cell was in overdischarged state.