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

Yoona Wagener is a tech editor, writer, and product reviewer.

Updated on June 21, 2024 Reviewed by

Southern New Hampshire University

Lisa Mildon is a Lifewire writer and an IT professional with 30 years of experience. Her writing has appeared in Geekisphere and other publications.

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What To Know

Go to System Settings >Displays > hold down the Option key > click Detect Displays.
Go to System Settings >Displays and check the resolution and brightness settings.
Also, check the display cable connections, and update adapter software if applicable.

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.

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

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

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

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

Show Thumbnails for resolutions highlighted from Displays settings in macOS.

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.

Increase your chances for success by avoiding daisy-chaining several adapters and cables together. Macs tend to work best with external displays when an Apple-branded or compatible cable and adapter are directly involved.

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Outdated drivers or software for docks.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.

How do I extend the display on a Mac?

To extend the Mac display, set up dual monitors on the Mac. Connect the monitor using HDMI, Mini DisplayPort, USB-C, or Thunderbolt ports. Position the monitors and power on the Mac. Open System Settings and choose Extended display from the Use as drop-down menu. Or, select System Preferences > Displays > Arrangement and uncheck Mirror Displays.

How do I make a monitor the main display on a Mac?

To set an external display as your main monitor, open System Preferences or System Settings > Displays > Arrangement or Arrange. One of the displays will have a white bar above it. Click and drag the bar to another display to set it as your main display.

How do I stop a Mac from turning off the display?

To prevent a Mac from going to sleep and turning off the display, go to the Apple menu > System Settings > Lock Screen. Or, choose System Preferences > Energy Saver > and move the slider to Never. Your Mac display won't turn off now.

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