I have several BlackMagic Intesity Pro cards and have seen this problem happen on numerous occasions (on each card on different systems).
Randomly, the card will preview or capture a black screen with no audio. The only workaround I have found is to remove the card from the pc and re-seat it.
I have the latest drivers downloaded from the black magic website v3.2 and have tried various forms of inputs including, 2x HDMI sources and Composite video but once it is in a state of no output - the preview or capture will always be blank. I am running the cards on Windows XP, Dual core processor with 2GB RAM.
I have searched through this forum and have tried everything suggested but I know my settings etc are correct because preview and capture is ok initially before it starts going blank.
Windows see's the card ok, my settings are all correct, graphedit loads the filters and renderers fine and it still captures the correct frames per second, all be it a blank screen!
Does anyone else have this problem? or is there another workaround rather than having to take the card out and in again?
I have somewhat of the same problem as you do. With my card I am only able to capture sources in 480i, anything above that produces black screen as you described. I have only been using composite and component because of HDCP. I have tried reseating my card once, reinstalling the drivers, all kinds of settings in control panel, and several different programs.
Another thing I noticed was that when I use the input processing and output processing in control panel, nothing changes.