I just recently purchased an Apple ATI Radeon HD 5770 for my Mac Pro 4,1. My mac pro is the 2 x 2.66ghz quad core cpus(8 Cores). I had a 4770 in the computer before the upgrade. I installed the Graphics card and my DVI port will not work. I plan on putting my 4870 back into my mac pro when I receive an adapter to split the power connector to two. (the 4870 has two power connectors.) If anyone knows why this is happening with my brand new card please let me know. I plan to run 3 displays off the 5770 right now only two work through the other two mini display ports.