I found a few DVI ports don't support HDCP (see google) and those don't work on many HDTVs. Sadly this nugget seems to cost folk a lot of lost time.
I have a Samsung 46" Series 6 LED TV Model number UA46C6900VF. In the HDMI/DVI port I have a DVI to HDMI cable which is connected to my laptop. The laptop detects there is a Samsung HDTV connected and allows me to choose 1920x1080 etc, but the Source List on the TV says "This source is not connected. Please check the connection again." Has anyone else had this same issue? I have renamed the source to DVI PC but that had no effect.