MacBook external display not working? What to check
13 November 2026 · Mac guides
You plug your MacBook into a monitor and nothing happens. Or the first screen works and the second one stays black. Sometimes the picture flickers, or the monitor says "no signal". Most of the time this is a settings, cable or compatibility problem rather than a fault, and you can sort it out at home in a few minutes. This guide covers the checks in the order we would do them, and how to tell when the problem is inside the Mac.
First, check how many displays your MacBook supports
This catches out a lot of people. Many Apple silicon MacBooks have a fixed limit on external displays, and no setting can get round it.
- MacBook Air and 13-inch MacBook Pro with M1, and MacBook Air with M2: one external display.
- MacBook Air with M3: two external displays, but only with the lid closed.
- MacBook Pro with Pro or Max chips: two or more, depending on the chip.
Newer models change these limits, so look up your exact model on Apple's tech specifications page (Apple menu, then About This Mac shows the model and chip). If you have two monitors on a Mac that supports one, the second will never light up through a normal dock. Adapters that use DisplayLink software can add extra screens, but they need a driver installed and are not ideal for video or games.
Safe checks you can do at home
1. Check the monitor and its input
Make sure the monitor is switched on and set to the input you are using: HDMI 1, HDMI 2, DisplayPort or USB-C. Many monitors do not switch automatically. If you can, test the monitor with another computer.
2. Try a different cable
This is the most common culprit. Plenty of USB-C cables only carry charging and data, not video, especially the thin ones that come with phones and accessories. Use a cable that is marked as supporting video or DisplayPort, or a Thunderbolt cable. Cheap HDMI cables can also fail to carry higher resolutions such as 4K at 60Hz.
3. Remove the hub or dock
Connect the monitor directly to the MacBook with a single cable or adapter. If it works directly but not through the hub, the hub is the problem, or it cannot handle the resolution you want. Some hubs only pass video through certain ports.
4. Try each port
On a MacBook with several Thunderbolt or USB-C ports, try each one. If you have a MacBook Pro with an HDMI port, try that too. If one port gives a picture and another does not, that tells us a lot.
5. Check Displays settings
Open System Settings, then Displays. If the monitor is listed, it is connected and the problem is in the arrangement or settings. Check it is not set to mirror a screen you cannot see, and try a lower resolution or refresh rate. If the monitor is not listed, hold the Option key and look for a Detect Displays button.
6. Restart and update
Restart the Mac with the monitor plugged in, and install any pending macOS updates. A monitor that was working last week and stopped after an update is worth reporting to Apple as well as testing on another cable.
Flicker, wrong colours or blank after sleep
Flicker on an external monitor usually comes from the cable, an adapter running at its limit, or a refresh rate the monitor does not like. Try 60Hz in Displays settings. If the monitor goes blank after the Mac wakes from sleep, unplug and reconnect the cable. If that works every time, a newer cable or a firmware update for the monitor or dock often fixes it for good.
Compare the problem with the MacBook's own screen. If the built-in screen also flickers, shows lines or goes black, the fault is more likely inside the Mac. Our guide to a MacBook that is on but has a black screen, in the Mac guides list, covers that situation.
When it is a fault in the MacBook
It is worth having the Mac looked at if:
- a known-good monitor and cable work with another computer but not with your MacBook, on any port;
- one port has stopped giving video and is also loose, or no longer charges;
- the problem started after a drop, or after liquid got near the ports;
- the MacBook gets very hot or shuts down when a display is connected.
On MacBooks, the USB-C and Thunderbolt ports are soldered to the logic board or to a small port board, and they rely on control chips on the board. A damaged port or chip can stop video while charging still works, or the other way round. These are repairable faults. Chip-level logic board repair often means the port or chip can be fixed without replacing the whole board. Liquid near the ports needs attention quickly, because corrosion spreads; see our liquid damage page.
Before you bring it in
Note which ports, cables and monitors you have tried, and what happened with each. Bring the cable and adapter you normally use if you can, because it helps us reproduce the problem. As always, back up your files first if the Mac is otherwise working. We also offer a full diagnostic if the fault comes and goes.
Get a quote
If your MacBook still will not show a picture on an external monitor after these checks, call 020 7394 2525 or bring it to 80 Willow Walk, London SE1 5SY. We are open 9am to 6pm, Monday to Saturday, with bike collection in London and courier collection across the UK.