Mac Boots to Black Screen with USB drives attached

My Mac Mini has started to boot to a black screen if I have my two hard drives attached. It’ll start booting as normal with the black screen and the white Apple and loading bar. However, once that clears, it’ll be a blank screen.

Pressing shift will boot it in to safe mode without issues and then sometimes if I reboot, it’ll boot to the login without issues, somethimes it goes back to the black screen. It used to be a black screen but the cursor would be present, but now it’s just black.

The Mac appears to boot fine without the drives attached.

Short of plugging the drives in each time I start the machine (and then throw some scripts together to start programs only once the drives are mounted), are there any steps I could walk through? A google hasn’t been much help - I’ve found one article that looks helpful, but isn’t - it tells me to boot to single user mode and run fsck, but it’ll initially show the terminal as it loads, but then goes black and I have to force reset.

I have had something similar with USB thumb drives and it was usually a sign that they were on their last legs and about to fail. Have you tried running anything like First Aid through Disk Utility? It could be that the USB drives have problems and this is stopping the Mac from booting.

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I hadn’t, as both drives are the same age as the Mac (just under a year) but it’s a good call, so I’m running it now.

You could try booting in verbose mode, by holding Cmd-V at boot.

I think @darranwest is probably right, that macOS is running fsck on a drive.

Have run through on both, it didn’t seem to show issues. Reboot, same issues.

Tried both rebooting with one drive attached and then the other - same issue.
I’ll try the verbose boot and go from there.

Hello @drezha,
After posting my initial replies I remembered a problem I had with an external USB hard drive. tl;dr, the issue was with the USB interface in the enclosure, not the physical drive. I am not sure if my problem was the same as yours, but more detail can be found below.

The drive in question would randomly unmount, cause OS X to say it needed initialising and would sometimes stop my laptop from booting. The drive was not that old but I just kept having problems with it. After getting more frustrated with the drive (and wanting to get some data off it) I eventually pulled the enclosure apart and found the the drive inside was a standard 2.5" SATA drive. I put it in my USB disk dock (similar to this one, and the drive mounted and worked without a problem.

Having got the data off I formatted and partitioned the drive several times, copied data to and from it, and rebooted the laptop without any issue. I then put the drive back into the original enclosure and the laptop would not start with it connected, it would unmount at random and OS X would sometimes want to initialise the drive.

From what I could see the drive was OK but the USB interface in the enclosure had some sort of defect. Having pulled the enclosure apart I felt I could not really ask for a replacement, and as the drive seemed OK I ordered a USB disk enclosure. The drive is still working today and I use it to move large video projects between work and home. Since I put the disk in a new enclosure I have not had any problems (am now touching my wooden desk surface while typing this). The same disk in a new enclosure does not unmount at random, MacOS does not want to keep initialising it and I can boot up my Mac with the drive plugged in.

As I mentioned previously, the problem I had may be different to the issue you are facing but the problem may not be with the actual disk in the enclosure. It could be with the USB interface that the drive is connected through. I was lucky that in my case the drive had a standard SATA interface so I could connect it outside of the enclosure. I am not sure if newer drives are not directly soldered to the circuit board inside the enclosure.

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That would be worth trying, as the SSD drive is a 2.5" drive that I have then placed in an enclosure. Not sure why the other drive might be causing issues, but I’ll give it a go, as that’s my Time Machine drive and if needed, I can use my Synology as the backup, or I have an external 3.5" drive that isn’t currently being used.

However, I haven’t had any issues with drives dismounting whilst in use.

So I tried using a HDMI connection today for booting the Mac, rather than the USB C output and it worked without issues at all, booted straight in to macOS without issues.

It may mean now having to change connections everytime I want to use my Windows machine unfortunately, but worth it for the hassle of not having to reboot my mac in to safe mode etc to keep getting it to work! Annoingly, I only bought this monitor as it has a HDMI and USB C connection - I’d have got a two HDMI one otherwise!