When both my HD cable box and my Samsung 841 DVD player are both "ON" I can't switch back and forth between the two. When I switch from one to the other, a message comes on the the screen that says the "DVI/HMDI output is blocked". Sometimes then I will get a picture on my TV, sometimes the screen will then remain blank.

I can usually resolve the problem by turning off either the DVD player or the cable box before switching over to the other signal.

Any ideas what's going on?

Troy