27" iMac won't boot after power outage

[jpfisher]

Just had a breaker trip and I was unable to start my iMac afterward the power came back -- I had the same exact issue a few weeks ago after an outage -- in a different apartment (so it's probably not the electric from the outlet at fault)

Hitting the power button causes the drive to spin up and fans to go on, but no chime and no screen.

Resetting the SMC does nothing. Same results.

However, I was able to remove two of the four SO-DIMM modules (the two on the right side) and the system booted. I powered it down and put the RAM back in and it booted fine.

Any ideas? Logic board? Did I just need to clear the RAM in order to get it to go? I've not experienced anything quite like this before.

 

[RollTide]

Has happened to me a couple of times. I unplugged it, hit the power button and then plugged it back in. Powered on like normal.

Sucks living at the end of a grid.

 

[rkaufmann87]

Do a SMC reset by:


SMC RESET

•*Shut down the computer.
•*Unplug the computer's power cord and all peripherals.
•*Press and hold the power button for 5 seconds.
•*Release the power button.
•*Attach the computers power cable.
•*Press the power button to turn on the computer.

 

[Bmaintz]

I am buying a 21.5 iMac on the refresh...
Run a APC power back up on my PC, we get a lot of bumps on the AC line but my PC never blinks, just keeps on going...

My new iMac will get plugged into the APC for sure...
Bob

 

[jpfisher]

If anyone runs into the same problem -- this was caused by a bad SO-DIMM. Apple replaced the memory over the weekend and it's working perfectly.

 

[nighthawkess]

Mac won't turn on after power outage

I had the same problem. No matter what I did. That being "holding the power button down, checking the breaker, unplugging and plugging it back in. Making sure there was in fact power to the plug itself, by plugging in a lamp. I found another post on the internet that said, "Unplug the mac from the back of it. Not from the plug in." Then reconnect the wire ...again at the back of the Mac. Worked great and turned on no problem. (I wonder if it's some sort of protection "thing"?" Hope this helps some folks who are experiencing the same thing!!

 

[ocean-girl]

I will try all this--I'm terrified that I have a hard drive that is zapped and a lot of writing wasn't backed up.
The power in my house went out in the morning, they were doing work on the poles and the electricity and turned it off, I was asleep, then back on later, my computer had been plugged in without a surge protector!!! I'm in a panic I hope not to loose anything, meant to use a surge protector and never did.
The power cord doesn't light up (I have a macbook air) green like it usually does when you plug it in
Sounds like it worked for everyone else I'll try all this, I'm in a panic.
It was sort of a shady electric company with a strange name, not the normal central one, I hope they didn't make a mistake and send some sort of extra boost that would zap electronics or ruin computers. I am not sure why the computer would just not start up, after power comes back?!!

 

[MacPlus85]

Mac won't turn on after power outage

I had the same problem. No matter what I did. That being "holding the power button down, checking the breaker, unplugging and plugging it back in. Making sure there was in fact power to the plug itself, by plugging in a lamp. I found another post on the internet that said, "Unplug the mac from the back of it. Not from the plug in." Then reconnect the wire ...again at the back of the Mac. Worked great and turned on no problem. (I wonder if it's some sort of protection "thing"?" Hope this helps some folks who are experiencing the same thing!!

Mac won't turn on after power outage

I had the same problem. No matter what I did. That being "holding the power button down, checking the breaker, unplugging and plugging it back in. Making sure there was in fact power to the plug itself, by plugging in a lamp. I found another post on the internet that said, "Unplug the mac from the back of it. Not from the plug in." Then reconnect the wire ...again at the back of the Mac. Worked great and turned on no problem. (I wonder if it's some sort of protection "thing"?" Hope this helps some folks who are experiencing the same thing!!

The key, as referenced above, is to unplug the power cable that goes into the back of the Mac. I had the same original problem, tried everything else and was about to take the machine in until I learned this. Voila!

 

[cynics]

If anyone runs into the same problem -- this was caused by a bad SO-DIMM. Apple replaced the memory over the weekend and it's working perfectly.

Consider a UPC. Not only will a good one offer you high quality surge protection and "clean up" the supply power but you can set it to safely shut down your iMac in the event of an outage.

 

[dwig]

Consider a UPC. Not only will a good one offer you high quality surge protection and "clean up" the supply power but you can set it to safely shut down your iMac in the event of an outage.

I highly recommend that ALL computers be connected to a UPS unless they have their own battery (e.g. notebook, tablet, ...) and then they should be connected to a good surge protector.

 

[Cmacrafton]

Since this is one of the first recommendations google gave me when researching this issue I thought i'd share my fix even though the thread is 10 years old it was on the right track for the newer models also.
My iMac wouldn't reset with the "unplug from the back of the computer for 5 seconds" suggestion. Mine actually was "unplug for 15 seconds, plug back in and wait 5 sec then power one" I used a timer so I could make sure to follow it exactly. Here's a link to the article that helped me. Which was buried in the search results.

Reset the SMC of your Mac - Apple Support

The SMC is responsible for managing power on your Mac. Resetting it can resolve certain uncommon issues related to power or thermal management.

support.apple.com