Base M4 mini booting from external Thunderbolt NVMe.
I set it to restart using the internal SSD.
Chime sounded normally but then nothing happened.
I held down the power button to switch off, disconnected the power and the external, reconnected the power and pressed the power button again.
Got the chimes but nothing else. Power button came on and off several times and then started flashing red.
Mac mini, macOS 15.4
Just to be clear, it is no longer booting at all, internal or external?
If that is the case you may need to do a Revive operation on the firmware and if that doesn't work you may need to do a full restore operation. Depending on the macOS on the older Macs you have, you will either use Apple Configurator or Finder:
How to revive or restore Mac firmware - Apple Support - for the working Mac running Sonoma or later
Using Apple Configurator to revive or restore Mac - explains both methods
The hardest part of the process will be getting the Mac into DFU mode which is generally made difficult because it is not something you want to accidentally enter.
Just another question, did this occur just after a macOS update? There have been a few occurrences reported in dual boot system that things went south after a macOS update with Sequoia.
Try this process: With Mac off hold down the power button until see it will start in recovery mode. From there you can use disk utilities to check drive and then restart by selecting the internal drive. I did this operation the other day for the same issue you have and it fixed the booting issue. When you do this you may need a wired keyboard and mouse.
Your solution seemed less drastic so I thought I would give it a go.
I did it, pressed the power button, got the chime but then nothing!
So I moved across to my M2 you tell you it hadn't worked when out of the corner of my eye I noticed the M4's monitor had the login screen and now everything touch wood (knock on wood) appears to be back to normal.
I reconnected the external boot drive and booted into that with no problem.
So thank you very much.
I'm just wondering whether this was a one-off glitch or something that's likely to recur.
Thanks for the info.
I was considering following it when tbirdvet's suggestion came through and actually worked, though with a few worrying moments.
What I found most strange was that I was participating in a thread about the same thing last week!
I'd like anyone's opinion on this.
I had difficulty booting into Recovery Mode.
I held the power button down for maybe a minute, the chime came normally (at the start) but nothing appeared on the monitor . . . no connection so I let go the button.
On a hunch I unplugged the monitor and plugged in another and was sitting back wondering what to do next when suddenly the Recovery Screen appeared.
So does Recovery mode usually take ages to appear?
I don't have an M4 Mac but my dual boot M1 MacBookAir comes up in a few seconds when the internal drive is set as the "default" boot drive and maybe 10-15 seconds when the external drive is the "default" boot drive. Also, with more drives attached, even non-system, it will take a bit longer as the boot loader in recovery waits to make sure all mounted drives have been checked for an OS.
What really hasn't been explained very clearly is that there are two recovery partitions on dual boot systems, one on each boot drive when external drives are used, one in each container if separate partitions are used on an internal, and one in each volume group if a single container/partition is used. So, if one boot system is say Sonoma and the other is Sequoia, if your default boot system is Sonoma, when booting into recovery, you will boot to the Sonoma recovery system and visa versa.
The default boot system is determined when you select the boot system in System Settings->Startup Disk. If you boot into recovery and select the boot system there, the default boot is not changed unless you enter recovery itself and select the startup disk from the Startup Disk menu.
I believe mine ws a one off issue as I had an app that was not playing well with my external drive causing the ejection and the Mac going blank. I removed the app (owc disk ejection feature). Never had that issue before and I hope never again.
New M4 mini refuses to startup and light is flashing white and red.
