Solved: MacBook Not Detecting External Monitor

Jump straight into the solution

Intro

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They say true tech wizards can solve any problem with a single terminal, but I’m definitely not one of them.

I use an M1 MackBook Pro hooked up to two external monitors.

The biggest monitor is for my IDE / web browsing, the smaller one is for AI tools, and the MacBook’s built-in display is dedicated to terminal.

Then one day, my trusty smaller monitor suddenly stopped working.

Verification

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• “Check if your MacBook is turned on.”
• “Check if the monitor’s power is connected.”
• “Check the cable connection.”

When you googled it, most of the posts are like this. Is there anyone who wouldn’t even check this?

I cross-checked with one other monitors and cables, and even visited the LG Service Center. The monitor / cable / Mac are all normal.

The strange thing was that the screen didn’t show up only when I connected “my MackBook” to “my monitor”. The monitor received a connection signal, but the Mac couldn’t detect the external display.

Apple Support

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The Apple support advisor told me to first try booting into Safe Mode¹ with the monitor cable connected. When I booted into Safe Mode, the Mac’s default wallpaper appeared on the monitor, but the top bar or the Dock didn’t show up, and the mouse cursor wouldn’t move over to it either.

The advisor said the phenomenon is one of the very rarely reported errors. The exact cause is unknown, but there is a possibility that the information related to the monitor got tangled or disappeared within the Mac System.

The advisor gave me two solutions: wipe and reinstall the OS, or create a new user account.

The advisor was kind, but the moment I heard this answer, I got really annoyed. WTF it mean to blow away all my settings just to connect a monitor?

When I said I absolutely couldn’t do either, they said there is actually a method floating around the internet, but if i try it and goes wrong, all the other monitors I am currently using well could completely stop working. Seriously, WTH?

I ended the consultation there because I thought I would make a scene if I stayed any longer.

Reddit

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While searching through Reddit, I found the following link.

The Apple advisor’s words that everything could stop working came to mind, so I hesitated, but there were quite a lot of related posts, and I couldn’t find any comments saying they followed it and got ruined.

First, I uploaded important files to the cloud, and proceeded with the resolution that it gets ruined, since I’ve used the Mac for a long time, I would set it up again from scratch over the weekend, and fortunately, I succeeded.

Solution

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The solution I found on Reddit was simple. They say that if you delete the tangled display settings file, /Library/Preferences/com.apple.windowserver.displays.plist, and reboot, the Mac will automatically initialize the settings file and recognize the monitor normally again.

FYI: sudo on Mac might require a password input.

0. Backup ( You don’t have to do it, but copied to home just in case)

sudo cp /Library/Preferences/com.apple.windowserver.displays.plist
~/com.apple.windowserver.displays.plist

1. Delete
```bash
sudo rm /Library/Preferences/com.apple.windowserver.displays.plist

2. Reboot

3. Pray (Most important!!)

Fortunately, perhaps the prayer worked, the monitor was recognized normally.

Final

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To some people, it might seem like just a mere computer problem, but to me, it was a nerve-wracking time.

If by any chance there is someone going through the same situation as me, I hope this post helps.

(If you cherish your Mac more than I do, I recommend proceeding after a Time Machine backup)

3-Point

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1. The monitor suddenly wouldn’t connect.
2. I was scared the Mac would break while resetting.
3. Google is Invincible and Reddit is god.