I have just bought the the same machine, but don`t have cable TV. However, I do have a Sky digibox and can record from it without problems. I assume you are getting a picture, but with no sound.
I have no knowledge about the cable TV boxes, but imagine that there is a Scart output. If so, check that your cable box and Scart lead are working OK, by plugging them directly into the TV scart socket.
If all is well, plug the Scart lead again into the Panasonic, ensuring a good seating. Check you have it set on the correct AV setting. Turn the TV to the AV number you use for the Panasonic output, and you should get both sound and vision. If not, try another Scart lead; perhaps there is an "iffy" contact on it. I would suspect the Scart lead.
If that fails, either contact your dealer or phone Panasonic on 08705 357357
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