What version of OS are you using?
What MacPro spec? and year?
What other cards do you have installed?
Is this an existing show - or are you starting from blank?
What drivers are you using for the Decklink Card?
Does the Deklink card work with supplied software outside of catalyst?

Check your drivers and test the Decklink card with supplied software
I would suggest try starting from blank catalyst show to see what happens


Simon