Hi, I have a MacPro 3,1 running 10.10.3 - it zooms along very well. I am using an Apple Cinema Display 20inch at 1680x1050. The native 2600 card was struggling so I have bought and fitted a Radeon R9 270X card, see screenshot. The increase in performance and usability is marked. However, when I switch on, I get the EFI boot screen and then, as OS X loads, it goes black. The only way to restore the screen is to disconnect and then reconnect it. It's absolutely fine thereafter. Does anyone have a fix for this, please?