I'm connecting a 13" MacBook Air to a Dell 22" screen using the Apple Mini DisplayPort to DVI Adapter, with an Apple Keyboard with Numeric Keypad plugged into a USB on the MacBook and a USB mouse plugged into the keyboard. Also, the MacBook is running off external power.
When I close the MacBook lid, I thought the Dell monitor would become primary and the MacBook screen real-estate would "go away." However, the MacBook screen remains primary and I can move the mouse pointer off the Dell screen and onto the invisible MacBook screen.
Am I misunderstanding how clamshell mode works?
Best Answer
According to Apple Support, the clamshell mode (lid closed) requires:
You meet all three criteria. The support article goes on to provide steps for both wired and bluetooth keyboard & mouse combos:
Perhaps you could try opening and closing the lid again.