iMac keeps going into black screen with only cursor visible

I have a late 2015 retina iMac running Mojave. Boot up disk is an external SSD. Three user accounts, with two of these having users file on the SSD and one on the HD.

Every couple of days when waking iMac from sleep the screen goes black/empty (but the Mac is still on). Can see the cursor but nothing else, If I press a key I get the error beep sound.

Any idea what is going on? Might it be to do with user permissions?

I think I’ve to reset the SMC and PRAM as per instructions.

Sounds like the external ssd gets diconnected on sleep. Is there a clone or other disk you can try booting from to check whether this is the case?

But it only happens occasionally, which is odd

It could be another user on the device has “prevent hd’s from going to sleep” set to off? It is my experience that sometimes log in order can have a bit of a strange effect on a mac. f.e. If my wife logs into the iMac first it will go to sleep but then won’t wake up for network requests, which it will do if I am the one that is logged in first.

So does this happen when you are the only one logged in?

Good test - I will try that. An interesting side issue is that only my account has users folder on HD.

that could actually be the cause. If your HD spins down, and the ssd can’t see it it will have to wait (sometimes a LOOOOONG time) for it to come back up.

Does the issue occur when you only log another user in, and not yourself?

I’ll test that over the next couple of days.

My brand new MacBook Pro (2018) with touchbar does this occasionally on shutdown. It won’t fully shutdown and leaves only cursor and black screen. It has only happened a couple times since I bought it and I haven’t gave it a second thought until I saw this post trending on the forum. For context I only have one user account.

Reset the SMC by unplugging EVERY wire from the iMac and hold the power button for 5Sec.
Reconnect power, keyboard and mouse and start the iMac again.

I have a 5 week old Mac mini that reboots to a black screen every time (but mine shows no cursor). It was purchased to process files and do backups so email is the only data stored on the 128gb SSD. Everything else resides on a 2TB external HD.

I’ve seen the same behavior on multiple iMacs and MacBook Pros & Airs over the past few years. Some machines have problems on a reboot if ANY external hard drives are attached.

I was never able to determine the problem, but if I disconnect the external drive my new Mac Mini reboots normally.

So I have made sure I logged out of the account based on the HD every. night and the problem hasn’t resurfaced.

So what I now need to do to solve it is to move that account to the SSD (but then repoint photos library and iTunes library at the libraries on the HD. I think I might start another thread about moving Home directory as it’s a different question.

Thanks all!

So, I moved by user account to the SSD. All seemed to be working and then this morning my partner says that she just tried to switch from my to her account and it went blank (backlit but no dark with display). So this would seem not necessarily to be an issue of the SSD boot drive not waking.

Back to the drawing board?