Hi, I have a 2011 Macbook Pro 13". I have been having problems with external monitors. I use the displayport connection. One of two things will happen. 1. I plug in the external monitor. The laptop acts as if the monitor is connected, but the external monitor is black (i.e. in sleep mode as if there is nothing connected) My laptop thinks that everything is OK; I can move my mouse cursor onto the external monitor space, but I see nothing on the external monitor. 2. The laptop hangs at the blue screen that is usually displayed for half a second when attaching an external monitor. It will just sit there forever like it is trying to attach, but nothing happens. When I unplug the connection is goes back to single screen laptop mode without a problem. I know the problem is not the monitor or the cable. My wife has a 2010 MBP and it works flawlessly. Any ideas?