The manual (page 48) indicates that you can only edit the name for inputs if there is an active input present - inputs with nothing connected would be grayed out. There's also a note at the bottom of that page which says "HDMI input can only be selected when the external device is turned on and connected via HDMI." Those two items make me suspect that the cable box either isn't recognized as a source (perhaps the HDMI output hasn't been enabled on the box presently), the cable is faulty, or the box is simply defective.