Connect TV

Trying to set up a TV in the spare bedroom.  We have a spare cable box from before we became empty nesters.  I reconnected the cable box to a TV in the spare bedroom.  I can turn the TV off and on with the Xfinity remote.  However, the TV is not displaying a picture.  I double-checked the connections, and the input source of the TV is set to the cable box.  According to our bill we are only paying for two boxes.  So I assume that this particular box needs to be reactivated somehow.  How do I go about doing that?