I am thinking the cable from the wall goes into the IN on the cable box. The cable that comes OUT of the comcast box and IN to the TV now needs to go IN to the DVD. Then another cable needs to go OUT of the DVD and IN to the TV. DVD should also be set for a different channel than the cable uses, ex. cable uses channel 3 on TV. DVD box should have a switch for channel 3 or 4? put it on 4 and use channel 4 on TV to play a DVD. Hope this helps! I try. :
