Macbook Pro suddenly stopped detecting external monitor

Question

sumudu1994 Author

Level 1

5 points

Macbook Pro suddenly stopped detecting external monitor

I purchased a Macbook Pro last month(February 2025) and have been using it with an external monitor connected to it and was working fine. Since couple of days ago suddenly the Macbook stopped detecting the external monitor. I am using the HDMI port to connect the external monitor. When connected, the monitor shows that it is receiving signal from the HDMI source but the display is black. I can see the backlight is on though. When I go to the display settings on the Mac it doesn't show that the external is connected(only the built-in display is visible). I was using MacOS Sequoia 15.3.1 when this happened(please note that in the same OS version the external display was working fine but this happened suddenly) and then hoping this would be fixed, I updated to MacOS Sequoia 15.3.2 but the issue is still there. I tried several workarounds such as unplugging and replugging the monitor, restarting, sleep waking the Macbook, using an USB-C adapter to connect the monitor, Re-detecting displays in display settings but nothing worked. I am certain that there is no issue with my cable or the monitor because I tested it with my Macbook Air & my Windows laptop and the display works fine. My Macbook & Monitor specs are as follows,

Macbook Pro Specs

M4 Pro(MX2Y3LL/A)

14 core CPU

20 core GPU

48GB Unified Memory

Display settings

Running at default Resolution - 1728x1117

Preset - Apple XDR Display (P3-1600 nits)

Refresh Rate - ProMotion

Monitor Model - Asus VY229HE

MacBook Pro (M4)

Posted on Mar 19, 2025 12:26 PM

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Answer 1

Mar 21, 2025 2:04 AM in response to sumudu1994

The Apple support helped me!

The solution was:

Disconnect monitor

go to: /library/preferences

find & delete files:

com.apple.windowserver.plist

com.apple.windowserver.displays.plist (if available)

Go -> option -> user library -> preferences -> by host

find & delete these files

com.apple.windowserver. + alpha numeric string

com.apple.windowserver.displays.plist + alpha numeric string (if available)

Empty bin

restart

reconnect monitor

In case of doubt call them, really helpful! :)

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Answer 2

Mar 21, 2025 6:28 AM in response to sumudu1994

The "approved method" that does NOT require you to fiddle in the guts of macOS is to invoke Safe Mode.

Safe Mode does a number of different things. On older Intel Macs, hold shift at startup, but have your userid and password at the ready.

A parade of unusual things happens.

• Your Mac loads just enough of the kernel to do a disk check. Then it proceeds to do a disk check. This can take an extra about five minutes.

• your userid and password are required, even if you normally auto-login. So have them handy.

• Your Mac adds ONLY a minimal set of Apple-Only extensions, Not including graphics acceleration extensions. Screen updates will therefore be wonky and slow, but it ultimately should be correct.

• Your Mac assumes defaults for as many settings as possible, including screen resolution. This is the key for re-setting the screen, but there is a little more to it: Resolution is likely to be lower and settings ordinary. Use this as a starting point to customize settings to your liking.

Any changes you make in Safe Mode will "stick" in regular mode after you restart.

• after restart in normal mode, your Mac will take slightly longer to start up [once] because it rebuilds some system caches.

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Answer 3

Mar 21, 2025 6:34 AM in response to sumudu1994

this article explains how to start in Safe mode:

Start up your Mac in safe mode – Apple Support (UK)

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Answer 4

Mar 19, 2025 5:22 PM in response to sumudu1994

ASUS display VY229HE appears to be a display capable of 1920 by 1080 with

HDMI input.

To use with a modern Mac at modest resolutions you should be using a Certified cable labeled PREMIUM. if used with a display close to 4K resolutions, the cable should be labeled ULTRA and is backward-compatible.