How to Fix It When a Mac Is Not Detecting an External Display

This article offers tips on the display settings and cable specifications to check to fix an issue with a Mac not detecting an external display.

How to Fix Mac Display Issues

Try the following fixes, in order, to try to get your Mac to recognize the external display.

1. If you're using a MacBook, try plugging it into power. Some power-saving settings restrict certain processes to extend battery life.

2. Make sure your Mac supports more than one additional monitor. You can check the supported number of displays by clicking the Apple icon System Settings > Help > your MacBook > and looking under Display Support or Video Support.

   On older macOS versions, click the Apple icon > About This Mac > Support > Specifications > Graphics and Video Support.

3. Double-check your cables. The first thing you should do is make sure your cables are both correct and secure. Confirm that any cords running between your Mac and the display are firmly connected to both, and ensure that the display is plugged in.

4. If the cables seem fine, try unplugging them for a moment and then plugging them back in. Restarting the external display may give your Mac a fresh shot at recognizing it.

5. If you're using an adapter, make sure that your monitor and cable combo is compatible with your Mac. Some Macs use only USB-C or both Thunderbolt and USB-C connections, while some Thunderbolt variations require a Thunderbolt-specific adapter.
   

   In the case of a dock, check its manufacturer's support site and download new drivers, if applicable.

6. Check your resolution settings by going to System Settings > Displays. Press and hold down the Option key. This combination will reveal a hidden Detect Displays option at the bottom right. Click this button so that your Mac can scan for a connected display.

   On older macOS versions, get to this option by selecting System Preferences > Displays > Scaled.

7. Choose different resolutions. Still in Resolution settings, Ctrl+click a resolution on the list > and choose Show Thumbnails. Select a thumbnail other than the default option to see if this prompts a change.

   You may see a radio button next to Scaled. If you do, choose a different resolution from this view.

8. Deselect automatic brightness adjustments. Under Brightness, uncheck the box next to or deselect Automatically adjust brightness and manually brighten using the toggle. If the external display's brightness is too low to register, this could resolve that issue.

9. Put your Mac to sleep for a moment, and then wake it back up to see if anything changes in the Display preferences.

10. Restart your Mac with the external display connected.

11. Finally, disconnect all of the cables, power off your Mac and the external monitor for a minute or two, and then reconnect the cables and turn everything back on. Repeat the steps in Display settings if the monitor still doesn't work.

Why Isn't the Mac Recognizing the Display?

Problems between Macs and external monitors can come from a variety of causes, including:

• Incompatibility between the Mac and the monitor.
• Faulty cables (or the wrong cables).
• Power-saving options in a MacBook preventing it from running an external monitor.
• Outdated drivers or software for docks.
• Incorrect settings in your Mac's Display settings, including brightness and resolution.