Clamshell mode on Macbook m3 worked with 2 monitors but doesn't anymore

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Clamshell mode on Macbook m3 worked with 2 monitors but doesn't anymore

I have a Mac Book Pro Nov 23 M3 Chip running Sequoia 15.6.

I have 2 LG monitors - one with a USBC charge port, the other an HDMI port.

Clamshell mode was working great! I would plug my USBC in, be certain it was charging, and then hook up my HDMI port and close my laptop and there we have it, 2 nice big monitors working in tandem.

Then, today because I have a different setup at work ( vs home ) I needed to test out a USB Hub Pro which I hooked up into one of my 2 usb ports. I then tried to connect the HDMI from my 2nd monitor into it -- and my 2nd monitor displayed a mirror image icon/message and I set it to extended display. That was pretty gross - HDMI to usb hub refresh rate was poor and was not sharp. Fine. I disconnected.

Now I cannot get clamshell mode with my 2 monitors working again.

I have restarted my machine. I have woken it up out of sleep mode. I have connected it just to the HDMI monitor and that works in clamshell but just one monitor. I have connected it just to the USBC monitor and that works in clamshell but just one monitor. Keeping it open works with the main monitor ( the laptop ) and whatever monitor I have connected....i just simply cannot get both monitors to work anymore.

When plugged into the USBC ( which shows it is charging ) I can close the laptop with the HDMI monitor hooked up and I can clearly see the level of blackness slightly get brighter on the monitor and the screensaver graphic goes away - it's connected and powered - it's just not showing anything - nor does it show as a display in system settings - nor does holding option in displays to detect displays and clicking work.

What have I done? Can I never use my 2 monitors with this macbook again?

MacBook Pro 13″, macOS 13.4

Posted on Nov 14, 2025 3:11 PM

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Answer 1

Nov 15, 2025 7:03 AM in response to Grant Bennet-Alder

if no joy after making certain your cables are adequate for the job,

For MacOS 12 Monterey and some later versions, some users got relief by deleting some preferences files, then Restarting.

To access the folder using Finder for the system-wide preference

Copy and paste this string into:

Finder > Go menu > Go to Folder

/Library/Preferences

then find and delete this file:

/Library/Preferences/com.apple.windowserver

-AND- To access the folder for your-user preference

Copy and paste this string into:

Finder > Go menu > Go to Folder

~/Library/Preferences

then find and delete whichever of these two files you find:

~/Library/Preferences/com.apple.windowserver.<UUID>.plist -OR-

~/Library/Preferences/ByHost/com.apple.windowserver.<UUID>.plist

-- where [~] tilde is an active abbreviation for "current user"

-- and <UUID> is a string of hexadecimal numbers unique to your system, grouped as 8-4-4-4-8 hexadecimal digits

Restart REQUIRED after these deletions.

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Answer 2

Nov 14, 2025 4:16 PM in response to pwhit8

<< a USB Hub Pro which I hooked up into one of my 2 usb ports. I then tried to connect the HDMI from my 2nd monitor into it ... >>

the Mac does not support TWO displays on ONE USB port out of the Mac. You did nothing wrong, except your expectation is not supported. Plug the second display into the HDMI port directly on your Mac, and live happily ever after.

OR substitute a genuine ThunderBolt Dock, which can support two displays provided they are of modest resolutions.

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Answer 3

Nov 15, 2025 7:00 AM in response to pwhit8

first step is to be certain your cables meet the increasingly demanding specs, especially for cable length:

for USB-C cables and adapter/cables, no more than 1 meter maximum length.

HDMI cables you want for HDMI-only Displays (higher resolutions than 720p TV sets) are marked as Certified with an anti-counterfeiting tag and are labeled:

"PREMIUM High Speed HDMI cable" or that + "with Ethernet" (up to 4K at 30Hz) --OR--

“ULTRA High Speed HDMI cable" or that + "48G" (supports higher resolutions and backward-compatible)

Cables with No Certification tags are good for your standard 720p TV set, and not much more.

HDMI was invented for HD TV sets. it works great at its original resolution of 720i or 720p. At higher resolutions, it quickly develops issues that are complex to solve, and the cables and adapters required to solve are NOT intuitive.

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Answer 4

pwhit8 Author

Level 1

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Nov 15, 2025 6:00 AM in response to Grant Bennet-Alder

That's the issue. I was, before I tried this funny business with the hub, doing just as you said, and it worked.

USB powering connected to one display. HDMI port directly hooked up to other monitor. Was working.

I cannot get it to work again doing exactly what I was doing before. I think my macbook got confused with the settings of trying to connect two monitors through 2 USB ports but one of them a hub with an HDMI connection and now I can't get it back working like before.

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