Marakanetz: Usually, it will say something about HDCP in the user's manual if it is included. If not, most copy-protected sources will not display. It will not account for your poor display with some DVDs as HDCP is all-or-none.
Unclejeff: I agree that would be better but the OP has a display with only DVI input and sources with HDMI output. He has no other choice.
Kal