Help...I upgraded this afternoon after constant promptings from Apple. Left Mac mini 2018 running went to dinner and two hours later black monitor screen that will not display I am so screwed and so mad. What can I do

These things happen, there's no cause for panic. If the computer is still running (You'll see a little light in the bottom right corner on the front of the computer) try pulling the monitor cable from the computer and after a couple seconds plugging it back in. Make sure the monitor is getting power. It you still see nothing, hold the power button for a slow 10 count. This will do a forced shutdown. Now press it as you normally would and it should restart with the display working.

Since none of us were there we don't know what happened with the upgrade itself. It may have completed and for whatever reason the display didn't power up properly on the restart. The upgrade may not have completed. So your next step will be to open System Preferences, look at the Software Update tab and see if there's anything waiting to be installed. If so, do try again. If not, the upgrade happened and should be fine.

Thanks Malcolm and dwb for your suggestions. But no joy. On a hunch, I borrowed a brand new HP monitor and guess what. It works. I also found the instructions on Displays (once I could see a screen) to try and reset my SamsungSyncMaster 940B monitor to default resolution - no, Samsung remained black. Yes, the update worked - now OS is Mojave 10.14.6.

Apparently Apple wants me to now buy a new monitor. Hence forth, automatic updates are turned off. I will not allow an upgrade until I have READ all that it contains. My old, perfectly working, Samsung display will be landfill and don't we all need more of that.

P.S. Apple - not all of us are into gaming and not all of us need super speedy refresh rates and mega resolution. We just need to get some work done.

No Apple doesn’t want you to buy a new monitor. Software updates shouldn’t break hardware and even an OS upgrade shouldn’t break a display. Can you access another computer to ensure the display still works? In my years as a tech I’ve seen some coincidences...like the display dying while an upgrade was in progress.

are you using HDMI, a dongle? What”s the display? VGA, DVI?

This happened to me once before and tried rebooting (holding the power button until light on Mac went out), unplugging the power cord (when powered down), unplugging the HDMI cable, and power cable to the monitor. But nothing worked then. I gave up and came back to it the following day and it was as if nothing was wrong. Today I also did the upgrade and after the Apple logo with the Progress bar went across the screen went black and I could/cannot get it back. I gave up and am going to bed. I don’t think I gave the HDMI cable/port on the Mac a few second divorce so your solution may work. I want to point out that the monitor has two HDMI ports that I use for the Mac and Apple TV 4K. The TV works fine even though the Mac produced a blank/black screen. The monitor says it is going into low power mode when I’m on the port with the Mac.

FWIW, I just went through this same exercise upgrading to Catalina with my 2018 Mac mini. The installer downloaded, and I saved a copy before running it. After running it, the mini went trough a number of reboots which were expected, but ended up with a blank, black screen. (I have a Dell 4K display monitor directly connected via HDMI.) It sat like this for about an hour until I decided to give up and power-down the mini and try again the next day. When I did power the mini back up, it still had the blank screen, but this time I left it powered-on for about 2 hours. Powered it back down again, and when powering it back up I was a bit surprised that it booted up to the Catalina Desktop being displayed on the monitor. My guess is that since I was unable to see what was going on, Catalina was still upgrading and that took a long time to accomplish. I did not have to disconnect/reconnect the HDMI cable or do a SMC reset. It just worked. The key, for me, is allowing sufficient time for the upgrade process to complete ... even in the "blind."

I have the same issue. Mac Mini won’t connect to my TV using HDMI cable.

i know it works because I can connect to my mac using my iPad through a remote software and tried to change resolution and all of that but nothing works.

unable to use my Mac Mini with my TV since Catalina release, and it was working fine during the betas...

mine did the same thing , right after it said it needed to reboot to install updates. Had no screen and the Mac mini got very warm and the network was going crazy along with drive I used for time machine. I tried all the steps tech support said to no avail. I was just about to take it in when I read about doing a reset . I had to have my magic keyboard connected via usb but held down control command r and p when powering up . Finally got the apple logo and released the keys. The video card then came up but a shut down again and I had to do the same thing. I ran clean my. Mac and did a restart and it booted up just fine. Afraid to shut it off now.. My iMac which is older 2014 came through the upgrade perfectly.

might try the reset thing and see if it works for you .

Well I took my Mac Mini (2018) to the Apple Store after work today and could not get an appointment until Sunday 2:30. When there is no picture I would have thought in the past it was a Hardware issue, but since it happened after/while installing an OS update I think it is a Software Issue.

I only have Apple’s Wireless Mouse, Wireless Keyboard, and Wireless Trackpad. This only leaves one button to press during startup; the Power Button. I cannot try anything but On & Off; which does nothing.

I do hear a beep after power up and press the enter key. Every time I press it or some other keys it beeps. So it has to be the display. Tried several HDMI displays and cables but nothing ever shows.

until Sunday...

get a usb to hdmi adapter , worked for me same problem

apple techs don’t know about this problem but the hdmi output port breaks with catalina . i bought a usb c to hdmi adapter and it works fine . staples has them

An update to my original post concerning Mac mini 2018, upgrades, and old monitors. Folks, thank you for all your suggestions...none worked. We tried another older monitor, an Acer, which was working on a Windows computer. It showed only 'snow' on the screen. I ended up borrowing a new HP monitor to finish my work. I have since bought a new monitor, an HP with a wider format, and there are now no problems. My old monitor had a 4:3 ratio- we (techie friend helping) think that Mojave 10.14.5-6 and above will not work with old ratio monitors. Could be crazy, but at least things are working and happily monitors don't cost as much as they used to.

My Mac Mini 2018 is about 6 months old. I upgraded to Catalina yesterday (19 October 2019, Brisbane, Australia) and the upgrade at first didn't work - and had a button that said 'try again', which (kind of) thankfully did work.

But, the list of applications that the Catalina upgrade initially listed as "would not work" after the upgrade was significantly less than the number of my loved applications that now have the white circle and diagonal line through them! Even applications I recently purchased!

So now I am searching around for how to downgrade to Mojave without killing my Mac altogether (thankfully I do use TimeMachine since my MacMini (2010) model just died at the beginning of the year. I learnt that lesson the hard way.

I don't want bells and whistles - I simply want a working computer - that plays the applications I paid for and I want to use.

This will be no assistance to you, but I hope it serves to warn others about Catalina's 'apps killer' component.

Usually unplugging the monitor cable from the computer for a few seconds will fix it.

I put my Mac Mini back into it’s box to take to Apple Support. Not sure if I’m going to the Apple Store or Micro Center where I purchased it. I think I bought support for it.

also when you get the usb c to hdmi adapter have the mac mini powered up and it should detect the monitor . then power down and back up and you should be good to go

my monitor is a brand new lg 4k and it did not work on the hdmi port