The base power might be disconnected. Please check that the power cord is properly connected to the unit and that the power adaptor is connected properly to the electrical outlet.
The unit might be out of range between the base and the cordless handset. Please move the cordless handset closer to the base.
If all above still cannot cure the problem, please unplug the base’s electrical power. Wait for 15 seconds and plug it back in. Then allow one minute for the cordless handset to link up again to the base.