HD picture is blown up

I have an Optoma h27 front projector and everything was fine until about a week or two ago. I turned on the projector and whenever I have the (TV) on which is coming through a dvi connection on the projector and an hdmi connection on the cable box the picture is huge. the heads of people are cut off at the top and the picture is cut off at the bottom as well. when I hit the guide button the small picture is diplayed correctly. Any advice would be appreciated, is this a problem with the cable box, the cable itself, or the projector.--The aspect ratio is set at 16x9 and the zoom level is at 1:85.