27" iMac shuts self down and will not turn on unless unplugged first

[simon3163]

My house has wonky electricity. I switched to a different power strip and my Mac Mini completed an update (without powering down) last night for the first time in months.

Hello, did this solve your issue?
We have just moved to British Gas (electricity) and their smart meters. Since this was done, i have been having random shutdowns and i think its linked to the new meters. My iMac shuts down, instantly, as if its lost power and like many have said won’t boot up without an unplug.

It seems to coincidental that this power shorts, cuts offs ect are happening as soon as the new meters have been installed. It really doesn’t seem an issue with the iMac, it runs flawlessly when its working!


Best Wishes,


Simon

 

[tantalos]

Just in case it helps anybody else, I've been having this same issue for months. My computer is a late 2012 iMac 27" running OSX 10.13.1 and it will go completely black and be unresponsive to any inputs, including the power button, until the cord is unplugged for at least 10-15 seconds and put back in.

I spent a couple months testing it and found that it never has the issue when I have only the thunderbolt plugged in. I would keep an external monitor plugged into one of them for a couple weeks and the error would never occur. Then, I started testing the USB ports individually and one by one 3 out of the 4 have had the issue. I'm now testing the 4th and I expect it will occur there eventually. USB port #3 took a few weeks to fail, which was surprising, but finally did it tonight after an update. Thankfully it didn't seem to happen during the update at least.

It drives me nuts, but I suppose I could perhaps figure out a workaround by having a thunderbolt to USB adapter. I'm currently testing the last USB with a wired apple keyboard, and have tested the other ports with a bluetooth mouse/keyboard dongle.

I've looked elsewhere for any info on this and had seen people saying that it had something to do with USB, which is what led me to this attempt at troubleshooting. I'm skeptical that apple would be able to help much from what I've read and the experience I had with support already. And since I bought this machine used and it's 5 years old, it's likely not worth dropping a significant chunk of change on a repair if I can do the thunderbolt to USB workaround.

Ugh, so annoying. Anyway, perhaps that'll help someone else with diagnosing this issue.

I know this is an old post, but I just read it today and signed up to macrumors today just to thank you for the really helpful info. My late 2012 imac had been bonking out (black screen and no signs of life) for months now and yesterday it started to get worse; happening 4 or 5 times a day. Each time I had to unplug and replug my monitor to get it going. I saw this post of yours, shut down my mac, unplugged all the usb ports and plugged my external drive using the thunderbolt plugin. My wacom tablet is plugged into the usb on my external hard drive. I left to go shopping a few hours ago and came back to a black screen, one tap on the space bar brought it back to life... I could not do that before. Time will tell if this is a good fix in the long run. Thank you. Thank you. Thank you a million times over.

 

[Machist]

I have 2011 mid iMac 21,5"
It randomly shutdown and I need to remove power cord few seconds and it will boot again.

I run tests -> ram/hardware is ok
PSU is changed, but still same issue.

Sometimes it work 2-3 days and now it shutdown immediately when I try open something.

 

[Machist]

Can that be GPU issue?
I think I try to change Nvidia GPU (flashed)