iMac won't turn on after power outage.

As the others have suggested you may need to have your computer repaired - the cost is unknown because we have no idea what circuits were damaged. Best case: power supply burnt out. Worst case: power supply, logic board and daughter board(s). Home owners insurance may cover the damage though depending on your deductible it might not be worth filing a claim. Due to a thunderstrike incident I have rider on my home owners policy that specifically covers damage to and theft of electronics equipment with a low deductible with replacement value. It adds $150 a year to my bill. Be sure to find an Apple Authorized repair center. Check here: https://locate.apple.com/pr/en/

Finally, there is one thing you can try. Unplug the power cord from your computer at the back. Hold the power button for a long 10 count. Plug back in and see if it will start. This is a long shot but I've seen it work on computers that were shut down by a brief power outage and wouldn't restart.

Unplug the power cord from the iMac, hold the power button in for 30 seconds, wait 30 seconds, then reconnect the power cord.

This will sometimes fix power interruption problems.

Take it to your local Apple Authorized Service Provider to be serviced. Chances are the power spike damaged hardware. At a bare minimum get a high quality surge suppressor or even better a UPS.

Hi, affinitywithfruits !

It is quite possible the iMac was hit with a power spike, which may have brought to the fore a problem with the power supply or logic board. The only way to tell for sure is to make an appointment to take it in to an Apple Store or Apple Authorized Service Provider.

I hope this helps, and good luck !

Hi again, affinitywithfruits !

The chances of your issue having a software cause are improbably low, bordering on the impossible. In all reality, it's probably a hardware issue where the only question to be answered is : how many things, at what cost, need to be replaced to make the iMac function normally? That question is best answered at an Apple Store or AASP.

In the future, I would put an uninterruptible power supply in place for the iMac to guard against voltage spikes. I have had some horrible experiences with APC in the past, but never had problems with Eaton UPSs.

Good luck !

Hi, BORg529 !

Sadly, surge suppressors do not work at protecting your electronics from a true voltage spike. I had this explained to me by a brilliant electrical engineer, but I will give you the short version :

An electrical spike will travel through surge suppressors, do their damage and leave, twice as fast as any home-level surge suppressor can react.

Which is why it is critical to have an uninterruptible power supply, which actively tames voltage spikes. Surge suppressors make you feel safe, but they do nothing to actually provide safety.

I hope this helps clear things up!

What other post said. But more importantly, do you have your iMac plugged into surge suppressor? It suppose to protect against voltage spikes.

I’m very sorry but my clairvoyancy began failing last Thursday.

Try read the reply from the OP, two posts prior to yours. OP did not have his computer plugged into surge protector, just straight into outlet. It could have save his iMac.

Don't snap at me! I said surge suppressor "could have" save OP iMac, not guarentee. Nobody knows how OP has his home, or work wired up.

Please go back and re-read my reply to you.