I have a full boat 2013 rMBP connected to a LG 34UM95 though thunderbolt and it has been working flawlessly for about 4 months. One connection from the laptop to the monitor and my external drives connected to the monitor. It has been great. Until today For whatever reason, my rMBP isn't detecting the monitor. It isn't showing up in preference or apple menu. I know the thunderbolt port is working as the drives are still visible that are connected to the monitor, but I can't run dual display or clamshell mode. I have rebooted several times, both the monitor and laptop. This sucks. Any suggestions? The searching I have done has revealed some NVIDIA card issues causing some challenges for others, so I hope it isn't anything like that.