Last night I installed the latest Apple updates (OS X 10.10.2 (14C1510)) on my 4,1. After rebooting, the DisplayPort on my Sapphire 7950 Mac Edition has stopped outputting a signal. The HDMI is still working. My monitor is a Dell P2715Q 4k that has given problems before but this doesn't seem to be its fault for a change. Anyone got ideas where I should start to look for a fix? I'm tempted to kill the windowserver.plist files but it would be good to know if there's already a known fix.