Vad60 is right-on. If you don't know the factory default PW, stop now and save yourself a LOT of nightmares and $$$$$$$$$$$$$$. I get the feeling you are a motel owner trying to save a little $. Look for cost savings in other areas.
And what was the result of the tests I asked you to try. You may have really cheap problems. When you try an IDENTICAL phone, make sure you use the line cord that is with the IDENTICAL phone.
We'll try to help you, but PW's are generally not available unless you can convince us that you are qualified to use them! Sorry.
John C.

When I was young, I was Liberal. As I aged and wised up, I became Conservative. Now that I'm old, I have settled on Curmudgeon.