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Please try this one check of functions: unplug the phone cord from the other phone, the one on the same line that actually works.
Then wait 2 minutes, after powering Off the problem Panasonic phone's base station.
Then after 2 minutes, power just the Panasonic/problem phone On again.
Check it's connection to the phone line.
See if there's a message on the Panasonic phone about the line, now.
See if you get a dial tone, can dial, etc.
What is the result?