MacBook only works with external monitor – built-in display stays black, keyboard not working

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MacBook only works with external monitor – built-in display stays black, keyboard not working

My MacBook (2021m 16 inch, Apple M1 Max, 32Gb, 1TB, Sequoia 15.6) still works, but only when I connect it to an external monitor. In that case, I can use it normally via the monitor. However, the built-in keyboard doesn’t work (it lights up, and the power button works), and the internal display stays black.

Here’s exactly what happens now:

When connected to an external monitor and turned on, I briefly see the loading screen on the MacBook’s built-in display, but then it goes black.
On the external monitor, the MacBook works fine.
If I try to turn it on without an external monitor connected, it doesn’t start — the display stays black.
The keyboard doesn’t respond at all, but it does light up, and the power button can turn the MacBook on or off.

What happened before this issue:

A while ago, I had my MacBook sitting next to the sofa, and it suddenly started repeatedly turning itself on and off without me touching it.

After that, I tried to start it normally — it would show the loading bar but then stop and shut off.

At one point, I attempted a reset (PRAM/SMC reset), and I briefly saw the reset-related window on the display once. However, since then, that screen has never appeared again.

Now, the only way I can get the MacBook to start is by connecting it to an external monitor.

Question:

Has anyone experienced something similar? Could this be a macOS/software issue, or is it more likely hardware-related (e.g., display connector, logic board)?

Any advice on how to troubleshoot or fix this would be greatly appreciated.

[Edited by Moderator]

MacBook Pro 16″, macOS 15.6

Posted on Aug 11, 2025 1:34 AM

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Answer 1

Top-ranking reply

HWTech

Level 9

67,064 points

Aug 11, 2025 5:43 PM in response to FelixNew

Sounds more like a hardware issue, but it is hard to say.

Try running the third party app EtreCheck and posting the complete report here so we can examine it for possible clues.

How to use the Add Text Feature When Posting an EtreCheck Report - Apple Community

FYI, there is no traditional SMC or PRAM Reset with the M-series Macs. The best you can do for a PRAM Reset is by using the following Terminal command to clear the PRAM (aka NVRAM):

sudo  nvram  -c

This command will prompt you for your admin password. Nothing will appear on the screen as you type the password, so press the "Return" key to submit the password. If you want to issue the command while booted into Recovery Mode, then omit the "sudo " portion or it will fail. This command may alert that some items could not be cleared such as the Computer Name. After successfully issuing the command, you need to reboot the computer so the system pulls in the default settings.

Another option would be to try a DFU Firmware Revive which resets the security enclave chip & system firmware. This should not affect the data on the internal SSD, but you should make sure to have a good backup just to be safe in case the process fails to complete. Unfortunately this process currently requires access to another Mac running 15.x Sequoia.

Also, try disconnecting all external devices just in case one of them is causing a problem.

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