I recently acquired a 51d5 and am having problems with a PC connection...
I have a 9600GT on my media PC with DVI-HDMI output to a receiver (Pioneer 1020), which sends then the signal to the screen. I also have DTV receiver running HDMI-HDMI to the Pioneer, then to the screen.
DTV setup is working fine.
PC setup will display my desktop background fine. It will display "easy" stuff fine (black text on white screen, google search results, etc.). When I play a DVD, it starts playing, for a couple seconds, blinks once, then I'm given a black screen (sound still plays). If I pull up forum websites (like this one), it does the same thing... (if I alt+f4 out of the application, the display returns). if I go to watch a .mkv or .mpg rip from my collection (digital copies are so much handier than physical media...), the same thing occurs... plays for a moment, then blinks out.
Anybody else seen this before? I suspect the cable is bad, so I'm replacing it. The video card has been fine before, even on 1920x1080 displays, so I think I'm ruling that out... is there an HDCP handshake issue going on? Any ideas?