You have a MacBook and an external display. You move a full-screen app from one to the other, and the screen you moved it from goes black. The Mac is still running and the cursor still moves, but that display is empty, with no desktop, no windows and no Dock.

It looks like a display failure. It almost never is. It’s how macOS handles full-screen apps and Spaces, and it can be fixed in seconds, then prevented with one setting.

What’s actually happening

On a Mac, a full-screen app isn’t just a big window. It gets its own Space, a separate desktop that exists only for that app. When you move the app to another display, macOS moves the app, but the display you left can still be sitting on the Space the app used to occupy. That Space is now empty, so you see black.

There is a second, related cause. If Displays have separate Spaces is turned off, all your displays share one set of Spaces. Put any app in full screen on one display, and every other display goes black, because the whole set of screens has switched to that app’s Space.

Get your screen back now

Try these in order; the first usually works.

  1. Switch Spaces on the black display. Move the cursor to that display and press Control-Left Arrow or Control-Right Arrow, or swipe left or right with three or four fingers. You’ll slide back to your normal desktop.
  2. Open Mission Control. Press Control-Up Arrow or swipe up with three or four fingers. The strip at the top shows every Space on each display. Click your desktop. If you see an empty full-screen Space, hover over it and click the × to close it.
  3. Leave full screen. Click the app and press Control-Command-F, or hover over the green button and choose Exit Full Screen. The Space closes, and the display returns to its desktop.
  4. Restart the Dock. The Dock process also manages Spaces and Mission Control. If the display stays black, open Terminal and run the command below. Your windows stay open; only the Dock and Spaces redraw.
killall Dock

The setting that prevents it

Go to System Settings > Desktop & Dock and scroll to Mission Control. Check these three settings:

  • Displays have separate Spaces: on. Each display gets its own desktops and full-screen apps, so full screen on one display no longer blanks the others. You need to log out and back in for this to take effect.
  • Automatically rearrange Spaces based on most recent use: off. With it on, Spaces reorder themselves, which makes it harder to predict where you’ll land after moving an app.
  • When switching to an application, switch to a Space with open windows for the application: on. Command-Tab then takes you straight to the app’s full-screen Space, wherever it is.

The trade-off of separate Spaces is that each display gets its own menu bar, and a single window can’t span two displays. For most people with a laptop and one monitor, that’s the better way to work.

Move full-screen apps the reliable way

Dragging full-screen apps between displays is where things usually go wrong. Two more reliable options:

  • Move the window before going full screen. Take the app out of full screen, move the window to the other display, then make it full screen there.
  • Use the green button menu. Hover over the green button and choose Move to followed by the other display’s name. On recent macOS versions, the same option is in Window > Move & Resize.

Consider Fill instead of full screen

If you use more than one display, you may not need full screen at all. Fill, with the shortcut Fn-Control-F on macOS 15 Sequoia and later, makes a window cover the whole display while keeping it on your normal desktop. There is no extra Space to get lost in, windows move between displays normally, and the menu bar and Dock stay where you expect. Our guide to Mac window management covers the other tiling shortcuts.

If the display is really off

If the black display shows no cursor at all, or the display’s own menu reports no signal, it’s a connection problem, not Spaces.

  • Unplug and reconnect the cable at both ends, or try a different port or cable.
  • In System Settings > Displays, hold Option to reveal the Detect Displays button.
  • Put the Mac to sleep for a few seconds and wake it; this renegotiates the display connection.

If displays often drop out after sleep or through a dock, see our guide to external monitor problems.

The short version

A black screen after moving a full-screen app is almost always an empty Space, not a dead display. Swipe or press Control-Arrow on that display, or open Mission Control and close the empty Space. To prevent it, turn on Displays have separate Spaces and log out once. On a multi-display setup, Fill is often a better choice than full screen.