Hi, So I have a 1,1 Mac Pro running El Capitan. I had been using it just fine for some weeks, but now I've run into some spontaneous issue. I was using my machine today (with my Radeon 5770), and I decided to change the refresh rate on my monitor. Well, the mouse pointer started skipping across the screen/lagging, so I was forced to just restart my machine. After replacing the boot EFI files again (since I couldn't boot from the darn drive for some reason), I was able to boot back into my desktop... HOWEVER, the OS no longer cares about my Radeon 5770. Expansion Slot Utility recognizes it, but the thing won't display a picture on any of my monitors. On the other hand, my 8800GT works just fine with it, and everything is displaying nicely. What happened? My other AMD card isn't working either. This all just happened in the blink of an eye.... any ideas?