Keep having problems with my iMac and Apple not responding! Tired of this situation! 7 shut downs in 11 minutes video. For the past week haven't been able to use it since just booting up will shut down! Today I disconnected it in the morning from the outlet and connected it back again in the evening and hasn't shut off yet but know will happen at any minute! Have called my Apple senior advisor and left 2 messages and nothing back from her... This is my 3rd apple (1 Powerbook, 1 MacBook Pro and this iMac) and its the worst!
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I had a similar problem on my 2015 iMac 27. Apple had me do all the usual troubleshooting steps: reset SMC/NVRAM, reinstall macOS, run Apple diagnostics, etc. Nothing was found.
Finally I took it to the Apple store and they ran overnight diagnostics which indicated a problem on the main logic board which was replaced. Since then it has run OK.
The Genius Bar has special long term hardware diagnostics they can run which may find otherwise undiscovered problems.
This is almost certainly a hardware problem, although I suppose there's a slight chance it could be a malfunctioning kernel extension. You can try Apple Diagnostics yourself but this is very limited relative to what Apple can run at the store: https://support.apple.com/en-us/HT202731
My problem was more difficult to troubleshoot since it only happened once every 1-2 days. Even if the special Genius Bar diagnostics don't find anything, you should be able to reproduce it right in front of them. However for a problem this frequent I think their diagnostics will find it.
Have you checked Console to see of any Kernel Panic reports, or system crash reports?
There's a long thread here about a similar issue to yours. Especially, the part about not having a Crash Report when your iMac restarts:
https://discussions.apple.com/thread/7525161?start=0&tstart=0
It could be a number of different things... looking under Console can help. I would check RAM and then, use the iMac with only Keyboard and mouse connected. Like, don't connect that external drive and pretend to do work on it or something for a while and see if you can replicate/isolate the problem...
For checking RAM, I think, Apple has a Diagnostics Test or Hardware Test that does it.
Did you upgrade the RAM on your iMac recently?
There's a long thread here about a similar issue to yours. Especially, the part about not having a Crash Report when your iMac restarts:
https://discussions.apple.com/thread/7525161?start=0&tstart=0
It could be a number of different things... looking under Console can help. I would check RAM and then, use the iMac with only Keyboard and mouse connected. Like, don't connect that external drive and pretend to do work on it or something for a while and see if you can replicate/isolate the problem...
For checking RAM, I think, Apple has a Diagnostics Test or Hardware Test that does it.
Did you upgrade the RAM on your iMac recently?
Thank you, will check on that. The computer is stock, haven't done anything. Was thinking about upgrading the RAM since it only has 8gb but first I want to get this problem solved before probably adding an extra problem.!
thx!
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Thanks for your response Joema, I also do have the same problem, it can be up and running for 1, 2 ,even 3 days and suddenly it starts to shut off. After uploading this video this past week I wasn't able to use the computer at all because it would boot and shut off immediately or sometimes even booting. I disconnected it from the outlet yesterday morning and pluged it at night and was able to work for a couple of hrs with no issues, did the same thing today and even though Im not running anything intense such as Lightroom or PS its working perfectly, still I know the main issue hasn't been resolved. Since we dont have Apple Stores in Puerto Rico just authorized resellers such as Best Buy I've been taking it to Best Buy and they haven't been able to do nothing on it.