Apple Cinema Display + MBP: how to get laptop screen on?

[btownguy]

I've got everything plugged in and have been working with the laptop screen closed for about an hour. I wanted to see what would happen if I opened the laptop screen and nothing happened - it remained off. How do I get both screens to run simultaneously?

 

[walnuts]

Go to the displays pref pane and do "detect displays" with your monitor open. I actually keep the displays menu on for that primarily. It should automatically change as soon as you open the computer, but detect displays should do it.

 

[JediMeister]

You must disconnect the external display with the computer in clamshell mode (screen closed) and reopen the display (normal usage) to revert the built-in monitor to the primary display. To run both screens simultaneously, connect the external display to the portable while the built-in display is not closed. This prevents the external display from becoming the primary output, and will give you the option of having the external display mirror or extend the desktop. Mirroring will match what you have on the built-in display, though probably at a lower resolution, extending will give you additional "real estate" to drag windows over to and manage your workflow more effectively.