Just started having this CC issue out of nowhere. I've tried everything I know, including the above. Holding the Menu button with Comcast box does nothing. I DID, however, get a white box to pop up holding another button on the box (of course can't remember which button now) and found a CC setting but didn't figure out how to make any changes to the "enabled" setting.
TV is Panasonic TH-42PX50U
Cable Box is Motorola DCX3400
Sorry. Fixed it! Here is the process in case someone else has a similar problem.
◦Press the Cable button and then the Power to turn the STB off.
◦Press the Menu button (on the STB).
◦Press the Down Arrow button until you get to Closed Caption option and then press OK to enable / disable captions.
◦Press the Power button twice to turn off the STB off and on again.