Below are some troubleshooting steps from Panasonic. I hope they can help!
a. Ensure that the telephone line cord and the AC adapter are properly connected.
b. Ensure that there are no broken pins on the telephone line cord.
c. Ensure that you are using the supplied phone lead.
d. If you are using a splitter to connect the unit, remove the splitter and connect the unit to the wall socket directly. If the unit operates properly, please check the splitter.
e. Unplug the phone from the electrical socket and remove the batteries from the base unit for approx. 30 minutes.
f. Disconnect the base unit from the telephone line and connect the line to a known working telephone, for example your neighbor's phone.