what are all theses coloured pixels on my iMac 27 screen ?
Coloured pixels all over my screen
iMac 27″, macOS 10.13
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Hi, Jacques1945...... do you have a smart phone of some kind with a camera built in, so you could take a screenshot and maybe post it here ?? you should be able to access the apple support communities from your smart phone, if it'll connect to Wifi, and most of them do.....and from there, you should be able to login and post a screenshot, so that I and we will know exactly what you're seeing and posting about.... did this just happen recently ? ..... I don't know exactly what year and type of iMac 27" you have, just that you have one, and you see coloured pixels on your iMac screen......you could try booting up into Safe (single() user mode and see if the problem goes away....you can do that by holding down the "Shift" key on startup....you'll have to be patient when doing this as it does a number of tests before it starts up in Safe mode....if successful, you'll see "Safe Mode" on your screen... otherwise, you could run Apple Diagnostics on startup, by shutting down, rebooting and holding down the "D" key on startup..... you should see a list of things on one side of your screen, then pass/fail on the other side..... you could try resetting the smc/pmu and zapping pram 4 times on startup....it's not hard to do and you can look up how to do it for pretty much any Mac (except the M1's---they don't need that and it won't work on them ) ...... if it just happened recently, all of a sudden....sad to say it might indicate a GPU failure. I'd try resetting the smc/pmu then zapping the pram 4 times first, to see if the problem goes away....if not, try Safe mode or running Apple Diagnostics...... that should confirm if it's a GPU failure or not.... if it is, then you'd have to contact your local AASP (apple authorized service provider) or make an appointment at your local Genius Bar in your nearest Apple Store, and in either case, take it to them, explain the situation politely, and see what they have to say.....
I hope you had/did/ do a backup of your Mac regularly....
good luck
John B