I have a MacPro 5,1 with 2 4TB internal drives and a 250GB SSD plugged in to a third party controller, booting from the SSD. 3 monitors connected. Previous versions have been fine, update proceeds normally. After update it bongs, gives me the loading screen then puts the loading screen in a portion of one monitor, other monitors have grey or black windows and it hangs. No keyboard modifiers seem to work - reset SMC, PRAM, Recovers, Shift, Option. If I disconnect the SSD it finds an old 10.7 install that it boots to just fine. My plan for tonight: Build a bootable USB Reconnected the SSD Plug the keyboard in to the front directly, not through a hub. Try option boot and run from the USB. Failing that I can format the SSD in another box (backed up before the install) and try a clean install. Any other suggestions? Or anything that I overlooked that would be an easy fix?