Check that the power cord is connected properly to the base.
Check that the power adapter is connected properly to the electrical outlet.
Move the handset closer to the base. It may be out of range.
Reset the base by unplugging the unit's electrical power.
Reset the handset by unplugging and re-plugging its battery pack. Wait for about 15 seconds and re-plug. Allow up to one minute for the handset to synchronize with the registered base again.