My iMac can’t start-up after power failure restored. What do I need to check?

Hi there,

Try this if your Mac is not starting up normally

Check power connections

Make sure that your power cable is undamaged and plugged securely into your Mac and a working electrical outlet.

If your Mac has no built-in display, make sure that your external display is connected to power, connected to your Mac, and turned on.

Press and hold the power button

Press and hold the power button on your Mac for about 10 seconds. (Every Mac has a power button. On laptop computers that have Touch ID, press and hold Touch ID.)

Then press and release the power button normally.

Unplug accessories

You could have an issue with one or more accessories or their cables. Unplug all accessories from your Mac, including printers, drives, USB hubs, and mobile devices. Then repeat step 2, above.

If you see something on your screen

If your screen shows a flashing question mark, circle with a line through it, or anything else, your Mac is turned on but isn't starting up:

If your Mac turns on but doesn't start up all the way

If you see nothing on your screen

If your Mac seems to be turned on but the screen remains blank, the issue could be software related:

If your Mac starts up to a blank screen

Reset the SMC (Intel-based Mac only)

If you're using an older, Intel-based Mac, resetting the SMC might help:

Reset the SMC

Contact us

If your Mac still doesn't turn on, contact Apple Support.

Additionally unplug the power cord from the back of the iMac for about 15 seconds. Plug it back in and try the Power button. If it starts or try to start (where before there was no response) then the power supply have been damaged.

If there's no response at all then follow Ronasara's recommendation and get an appointment at the nearest Apple Genius Bar or Apple Authorized Service Provider.  

I am going to guess that you did not have the computer connected via a protective electrical device and when the power came back on, your Mac was hit with an electrical spike which has damaged it. Take it to an authorized Apple service technician to get it tested and repaired, if possible.