Frozen iMac, plus can't run diagnostics

[LammaIsland97]

Hi everyone,

This is a bit of a weird one (the computer, not me!) - from time to time, my 2020 iMac (3,3 GHz 6-Core Intel Core i5) will freeze in the middle of tasks, I then wait for maybe 20 seconds, this screen flashes up, image below (looks like a seat pattern on the London Underground), then it sometimes reboots, or goes to the login screen. Once I log in, it asks me if I want to open all applications I previously had.
I have tried to run diagnostics, as people have said this is what I need to do to find out what is causing this, but then something else strange happens. The first black screen I see after holding down D when I boot asks for (I assume) my wifi password - but when I enter it (and I've checked it several times), it thinks about it for a second, then does the little shake from side to side, & clears the field.

So even if I wanted to run diagnostics, I can't seem to.

Does anyone know what might be causing A) the freezing, and B) Why I can't access diagnostics? Thanks very much in advance. Here's the screen I see after it has frozen, aka, London District Line seat pattern!

 

[TonyAguila]

Hi everyone,

This is a bit of a weird one (the computer, not me!) - from time to time, my 2020 iMac (3,3 GHz 6-Core Intel Core i5) will freeze in the middle of tasks, I then wait for maybe 20 seconds, this screen flashes up, image below (looks like a seat pattern on the London Underground), then it sometimes reboots, or goes to the login screen. Once I log in, it asks me if I want to open all applications I previously had.
I have tried to run diagnostics, as people have said this is what I need to do to find out what is causing this, but then something else strange happens. The first black screen I see after holding down D when I boot asks for (I assume) my wifi password - but when I enter it (and I've checked it several times), it thinks about it for a second, then does the little shake from side to side, & clears the field.

So even if I wanted to run diagnostics, I can't seem to.

Does anyone know what might be causing A) the freezing, and B) Why I can't access diagnostics? Thanks very much in advance. Here's the screen I see after it has frozen, aka, London District Line seat pattern!

View attachment 4596

Is your keyboard Bluetooth? Do you have it connected to USB when you try to boot into diagnostics? It seems like you will need to reinstall macOS from Recovery. Your iMac is fairly new so I don’t think it’s a hardware problem—but you never know. My 2018 Mac mini’s Bluetooth system went bad after a few weeks, and even Diagnostics could not report it. I had to bring it in to an Apple Store to prove to them that it was broken. They did a couple more stupid things afterwards that I don’t care to elaborate on.

 

[LammaIsland97]

Cheers Tony - I managed to run diagnostics, and as I tried it I thought "this won't work" but it did.
I'm in Austria, so my bluetooth keyboard is QWERTZ, however my wifi password features the letter Y.
Previously, the password wasn't accepted, so I treated the keyboard as if it were QWERTY, pressed Z for Y, and hey presto, it worked!

Ran diagnostics, "no problems detected" - but the freezing continues. No idea.
Thanks for getting back to me. I am reluctant to take it to the Apple store, it takes AGES to get it back, but maybe I just need to do it and grit my teeth.
Thanks again.

 

[TonyAguila]

Cheers Tony - I managed to run diagnostics, and as I tried it I thought "this won't work" but it did.
I'm in Austria, so my bluetooth keyboard is QWERTZ, however my wifi password features the letter Y.
Previously, the password wasn't accepted, so I treated the keyboard as if it were QWERTY, pressed Z for Y, and hey presto, it worked!

Ran diagnostics, "no problems detected" - but the freezing continues. No idea.
Thanks for getting back to me. I am reluctant to take it to the Apple store, it takes AGES to get it back, but maybe I just need to do it and grit my teeth.
Thanks again.

Since there are no apparent hardware defects, you should first try reinstalling macOS. Your model should be able to run macOS Ventura. Are you on Ventura? You can install/reinstall Ventura from Recovery. Your model would have come with macOS Catalina, which you probably have already updated. If for some reason you do not wish to install Ventura… yet, you can download the macOS installer file of your choice from the App Store. Do a search for “macOS [your choice]” and when it comes up, choose and it will bring you to its page. Click on Get and it will start downloading the installer into your Applications folder.

On completion of the download, it should automatically launch. My suggestion is to quit, for now, so you can secure a copy of the installer file to a separate location, and then you can again start the installation from the copy in your Applications folder.

Needless to say, this assumes you have a full backup of your system. And you keyboard should be connected to the Mac, not wireless. Cheers!

 

[LammaIsland97]

Thanks Tony. I guess it goes without saying that I'd need to re-install everything like Adobe Cloud etc. But it's a small price to pay to get everything working again. I have Ventura, so probably best to update to the latest. Thanks again, I'm going in!

 

[TonyAguila]

Thanks Tony. I guess it goes without saying that I'd need to re-install everything like Adobe Cloud etc. But it's a small price to pay to get everything working again. I have Ventura, so probably best to update to the latest. Thanks again, I'm going in!

NOT AT ALL! A simple reinstall of macOS will only affect your system, not your data. If you want to be more thorough, you could, from Recovery, completely erase your drive, and you can bring back all your data from your backup. Default is Time Machine, of course, but I rely more on Carbon Copy Cloner for migrating my information since it works faster, and better, in my opinion, than Time Machine. Nevertheless, I always have two Time Machine drives for redundancy, in addition to the clone, which gets executed automatically, several times a day—located on a separate SSD drive.

I repeat, there is no need to reinstall your data volume, unless you elect to. And even if you have Ventura 13.2 installed, you can re-install the same version over it. That’s the reason for making a copy of the installer file—for future re-installs without have to re-download it.