Power outage shut my iMac down

Try holding down the power button for 10-15 seconds and see if it starts up normally. If it does not, please book an appointment at your local Apple Authorized Service Provider.

Apple Authorized Service Provider Locator (AASP) & Genius Appointment

See if you cab unplug the power cord from the back of the iMac for about 15 seconds, plug it back in and try the Power button again the iMac will boot up? If it does then the problem is a failing power supply. I've been there - done that.

I had exactly the same problem, except after several attempts, the iMac would suddenly shut down and finally not turn back on at all. I made an appointment at the Apple store where I purchased the iMac (Oct. 2021) and they ran tests and fixed it. Said they might have to "change a chip". I recuperated it the next day.

Since then (been 3 weeks) it seems to work fine, but today there was a fleeting, barely noticeable power outage—some appliances did not even turn off—and the iMac had trouble again turning back on. But after disconnecting everything and waiting 10 seconds, I was able to pwer it back up and so far it has not shut down all day.

My question is, is there something I can install to protect the iMac from sudden outages like this? It's an uncomfortable feeling that I could lose access to my computer at any time because of an outage. The last time three weeks ago was a mega waste of time.

Thank you for your help!

You purchase a quality surge protector that your Mac is then plugged into, or an Uninterrupted Power Supply (UPS) that is compatible with macOS and that continues to provide current to your Mac when the power is cut. Then you shut your Mac down until power is restored, if not longer than the UPS battery provides.

My Macs are also configured to not automatically power up after a power disruption as often, that is a sporadic return to service with additional outages. Only after power is restored and appears stable do I then power up the Macs.