Cable box is plugged into denon's hdm1, but I can't get a picture. Hdm1 out monitor (arc) is plugged to TV hdm1 in (arc).

Power up all components. Select the HDMI 1 input on the Denon amp, and the HDMI 1 input on the TV. Additionally, run the old analog cables between the cable box and the TV. If no picture, select the input on the TV that is associated with the analog input from the cable box. You should have a picture at this point - but it will be a standard definition type. Check the settings on the cable box to change the output from "A / V" to Digital on the HDMI jack - if present. You may have better luck unplugging power / replugging in the cable box first - or calling the cable company if you can't find settings for this. Once you have the output of the cable box to HDMI, select HDMI on the TV. If you still don't have it working - try bypassing the Denon and go directly into the TV from the cable box. Try it with BOTH HDMI cables. Also - try different inputs and out puts (HDMI 2, HDMI 3, etc.). Discard any HDMI cable that fails to show video and play audio.