Hello & Welcome,
I'm Greg and will do my best to assist you today.
Sorry I didn't see your question earlier and to hear of any issue you are having with your phones.
To help you with this issue, may I ask:
1) The FULL Model Number of the phone system you are working with? If this is a cordless system, that model should be printed on a sticker on the bottom or back of the main base unit.
2) How many TOTAL cordless handsets do you have with this system?
3) Did this cordless handset come with the base unit - as part of a "package"?
4) You mentioned "Changing the base w/ other phones" - what "other phones" exactly were "changed"?
OK - is this a SINGLE Cordless handset that is not working? In other words, do you have THREE WORKING cordless handsets, but one that is not?
Also, can you double-check the model number PRINTED on the MAIN BASE UNIT, as I need to CONFIRM that model.