Re: Denon 3808 video probs???
It is unlikely, some cable boxes and/or companies do not activate the HDMI or DVI-D ports on their units. I had one like this and could get it to work for often months at a time by unplugging the cable box and letting it reboot itself.
Another option is to do a google search for the model # of the cable box and see it you can find the service menus to activate the DVI port (some have it, many are controlled via the RG6 from the cable company.
Ken Taraszka, MD