I'm having an issue. I like to use my macbook with a Dell External monitor, but also at times like to use the macbook in clamshell mode. Most of the time, I'll have the external display set as the main monitor (with menubar and dock). So if I want to close the macbook and use the display it works. But when I open the Macbook back up, the monitor doesn't come on. I have to go to detect displays in sys pref. to turn it back on. Any tips?