Macbook Pro M4 stopped recognizing second monitor after one month

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britb13 wrote:

I've been running two pretty standard 24" monitors with my Macbook Pro M4 for about a month. One was connected via HDMI to Thunderbolt, and the other was connected HDMI to HDMI. For whatever reason, one morning I turned on my laptop, and it no longer would recognize both monitors in the Displays section. It'll only show one at any given time. I've tested every single cord, both monitors, everything possible and still only one screen. This isn't a resolution issue as I'm not using high-res monitors. This is driving me nuts, and I desperately need my second screen for my wfh job. Anyone got advice??

Verify your software is up to date…

The current stable release of Sequoia including bug fixes, security updates is macOS 15.5

Keep your Mac up to date - Apple Support

Keep your Mac up to date - Apple Support

For your use, you would need certified cables labelled ar least "PREMIUM"

"Premium" in the context of HDMI cables is a magic word that it meets the required standards.

https://www.monoprice.com/Product?p_id=15427

If you think you will be using displays as large as 4K and want resolution higher than 30 Hz, buy "ULTRA" cables, which are fully backward-compatible.

https://www.monoprice.com/product?p_id=42674

M4 (plain) supports up to Two fully hardware-accelerated External displays (three for Mac mini)

that Hp display is a 1920 by 1080 display 60 Hz refresh rate

Interfaces include:

1 x HDMI

1 x DVI-D dual link

I x analog VGA

that LG display is a 1820 by 1080 display

interfaces include:

2x HDMI

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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.

What model-year MacBook Pro including what type processor {plain, PRO, MAX, ULTRA}

24 inches just tells the diagonal screen size. Far more important issues are resolution and refresh rate.

What Make&model display(s)?

There have been reports in these fiorums of problems with second monitors after installing recent Sequoia updates. Some claim that deleting a certain preference file and restarting the Mac (which presumably causes the Mac to regenerate the preference file) fixes it.

For the resolutions you are using, almost any reputable company's adapter USB-C to HDMI should work. Length should be one meter or shorter on the USB-C side.

HDMI at these resolutions uses a different signaling technique that is not severely length limited until you exceed 4K @ 30 Hz.