CrackMacMac not detecting an external monitor? Fixes that work
Check three things before anything else. The monitor is set to the right input, the cable actually carries video, and your Mac hasn't hit its external display limit. Those three explain most "no signal" problems. If they're fine, hold Option in Displays settings and click Detect Displays, then work through the rest of this list.
Quick checks
- Input. Use the monitor's own buttons to select the input your cable is plugged into, HDMI 1, HDMI 2, DisplayPort or USB-C.
- Cable. Many USB-C cables, including some that come with chargers, carry power and data but no video. Try a cable sold for video, or a USB-C to HDMI adapter.
- Port. Try another port on the Mac and the monitor, and plug the monitor straight in, without a hub.
- Accessory permission. Recent Macs on Apple silicon ask before allowing a new USB-C accessory to connect. If you missed the prompt, unplug and reconnect, or change the setting under System Settings, Privacy & Security.
Make macOS look again
Open System Settings, Displays. Hold the Option key and a Detect Displays button appears. Click it. Then turn the monitor off and on, and if that fails, restart the Mac with the monitor connected.
Know your Mac's limit
| Mac | External displays |
|---|---|
| MacBook Air M1, M2 | One |
| MacBook Air M3 | Two with the lid closed |
| MacBook Air M4 | Two with the lid open |
| 13-inch MacBook Pro M1, M2 | One |
| MacBook Pro with Pro or Max chips | Two or more |
A second monitor on a one-display Mac won't show up however you connect it. Adapters that use DisplayLink software get around the limit.
Still nothing
- Update macOS. Display detection bugs, especially after sleep, are fixed in point releases.
- Start in safe mode. If the monitor works there, a display utility or login item is interfering.
- With the lid closed, the Mac needs power and an external keyboard or mouse. See clamshell mode.
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Quick answers
Why won't my Mac detect my monitor?
The most common causes are the wrong input on the monitor, a USB-C cable that only carries charging and data but not video, a full display limit on base M-series Macs, and a USB-C accessory waiting for permission.
How many external displays does a MacBook Air support?
Base M1 and M2 MacBook Air and 13-inch MacBook Pro models support one external display. The M3 MacBook Air supports two with the lid closed, and the M4 MacBook Air supports two with the lid open. Check Apple's tech specs for your exact model.
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