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I was using Win 10 on my 2017 21.5" iMac before, but formatted it and installed Mac Mojave again. Here format means I've formatted the data disk as well as system disk, merged all partitions and make only one volume. And installed Mojave.

Now if I select "Shutdown" in the Finder menu the Mac always automatically restarts instead. I am using power button to shutdown the computer. Sometimes, the computer restarts itself - without any action. Weird.

How can I fix or diagnose this?

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  • This is a clean install of Mojave or did you restore from backup? Did you restore your data from backup (like in Migration Assistant)? – Allan Jan 7 '20 at 4:09
  • This is a clean install, yes. I formatted my harddisk and installed with mojave USB. – ʎzɐɹƆ Jan 7 '20 at 16:56
  • No, no data and the computer is empty right now. Just installed mojave and no other actions so far. – ʎzɐɹƆ Jan 8 '20 at 4:32
  • Ok. That tells me you didn’t bring over any “suspect” software. Now, using a Terminal enter this command sudo poweroff. This will shutdown the computer so be sure your apps are closed with everything saved that needs to be saved. – Allan Jan 8 '20 at 5:06
  • sudo: poweroff: command not found – ʎzɐɹƆ Jan 8 '20 at 9:17
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I used to work as an Apple technician and I'v had several Macs that describe your issue, but they were only laptops. The issue with them was liquid damaged. Now you thinking how the h'll can an iMac get liquid damaged, but I can tell you, I'v actually seen it myself. So it's possible but maybe not in your case.

I recommend to let an Apple technician look at it. Water damage causes a fault in the circuitry, but the same fault can happen from other causes or just rare breakage.

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    But here is a question. I've got some friends who are using the same computer and the same OS, everybody has got the same issue. All are damaged? – ʎzɐɹƆ Jan 12 '20 at 0:50
  • What circuitry would need to be damaged to prevent ACPI from telling the SMC to power off the machine? If there was actual damage as you describe, it’s much, much more likely (orders of magnitude more) that the Mac would not turn on in the first place. – Allan Jan 12 '20 at 10:09
  • @Lumi Could you tell me the exact example what you've experienced in the past? – ʎzɐɹƆ Jan 12 '20 at 12:46
  • I'v had several MacBook Airs that have been exposed to some kind of liquid. People came in with them because they where afraid for it to get worse or something.. but one thing I noticed was actually that some of them couldn't shutdown, even though I selected Shutdown in the menu. They immediately started again (looked like it rebooted).. I removed battery and plugged power in and they auto started. – Lumi Jan 13 '20 at 17:39
  • And about the liquid damaged iMac, the guy who had it said: The next day it was all fogged inside the screen.. he had his iMac next to a window, I don't know how close/far from it was or if he left the window open while it was rained outside, we couldn't know, he was assured that the window was closed so we had to believe him. The iMac was still working, we cleaned it and I haven't heard anything from him – Lumi Jan 13 '20 at 17:45

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