Hello & Welcome to Just Answer,
I'm Greg and will do my best to assist with this issue.
Sorry I didn't see your question earlier and to hear of any issue you are having with your phones.
If you still need help with this issue, may I ask:
1) If you disconnect the PHONE CORD from the MAIN BASE of the Panasonic system, does the text on the display CHANGE to something like "Check tel line"?
2) Is the OTHER CORDED PHONE (that does get a dial tone) connected to a DIFFERENT PHONE JACK -perhaps in a different room?
3) What landline phone service provider (phone company) you have for this phone line?
4) Do you have to a DIFFERENT phone line - such as a cell phone - and if so can try a TEST CALL to the landline number (let me know what is heard if you can make that TEST CALL)?
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