If you've purchased certified High Speed HDMI cables from a reputable manufacturer then I doubt it's the cables. Is there any difference, according to the Samsung manual, between the HDMI inputs 1-4 on your tv? If you Xbox works fine on all 4 HDMI inputs then I would suspect that there's something with the Comcast box (output settings?). However, organizing and cleaning up your cables/wires in the back wouldn't hurt and is probably not a bad idea. Less clutter, mo better.