I purchased a CS6829-3 handset at a second hand store that was registered to another number. It charged well. I did the de-register routine, and that cleared my two current phones, but would not clear the new -3. It still displays Out of Range or No pwr at base. I have left the battery out of the handset, and at the same time de-powered the the base for an hour. No joy. Is there a routine to do a factory reset, or get back to the register screen?