Note that the latch for opening the phone and extending the antenna is the same for both.
Rubber Keypad is Unresponsive
The battery might need to be charged. Charge the battery in the unit's receiver, the Panasonic KX-T4000H.
If the phone turns on but the buttons still do not work, the motherboard could be damaged. For instructions on how to access the motherboard, look through the Removing the Back Panel of the Phone guide.
If you are having issues with reception, try moving closer to the receiver, the Panasonic KX-T4000H.