Loss of non-hd channels

We have three hd cable boxes-DCH3416-each at separate rooms.  At one room, the hd tv is only able to show hd channels (1200, 1300, etc) not the non-hd channels (200, 300, etc.).  I've tried the rest of the tvs at the other rooms and the non-hd channels shows perfectly well.  I've tried to exchange boxes and turned on and off both the tv and cable box.  The same result, that one single room cannot get the non-hd channels.  Is this because of a weak signal?  Incidentally, the cable box is connected to the hd tv with hdmi cables.