1) Are you subscribed to HD service? Can't see HD without an HD feed. Digital cable isn't the same as high definition. You may need to upgrade as an optional extra. If so, it will be worth it.
2) Panasonic model number? Check your operators manual to see exactly what it says is the resolution/s provided. Read the set up instructions carefully. Even if you are getting HD from your provider & the Panny is HD (that is - offering 720 &/or 1080), if everything isn't set up quite right, you could be crippling the signal by one little detail not being set correctly.
Hooked up my new Panasonic Plasma. I ordered digital cable through my provider and that is obviously working. But I don't think I have HD...the HD channels all look good, but not outstanding and they all have grey bars at the top and bottom of the screen....I seem to remember that that indicated you weren't watching a HD broadcast on a HD channel.
And if it ain't working....any ideas on why not?