Switching the monitor on 2 seconds after the chime is fine. The system definitely will start with the 7950 in Mac mode, with the monitor switched off and the Displayport in either socket.The system definitely won't start with the 7950 in Mac mode, with the monitor switched on and the Displayport in either socket.The symptoms are that the Mac just won't boot if the monitor is switched on. Mac Pro 4,1 with Yosemite 10.10.1 and Sapphire 7950 Mac Edition I've just taken delivery of a Dell P2715Q 4K monitor and there are definite problems.