Why is my imac shutting down by itself?

I am having an issue with my iMac 2011.The screen keeps shutting down.It turns black so often that even before it logs in it will turn off.I have this problem since July 2016 and I have brought this iMac for repair for 5X.The last time was this December 2016.The apple technician will say a lot of different issue from the logic board, power supply, software problem and LCD screen.They seem not to fixed the problem.I really doubt apple capability to fix this problem.Funny every time you go to this particular store at friendly center and check my iMac, You will second doubt yourself because they will say they did not see any problem.So several times I need to go back again reassert my point.I am going to bring this again for the six times and see what happen.One thing I am sure if they can't fix this " I will never buy any apple device ever ".I taught it is worth all the hard earn money you put on this device because of its reliable.I paid for the repair and they never get it fix.So I will keep you posted people.

Has the memory replacement for your late 2012 imac helped, since your post in September? I am experiencing the same issues as you (and everyone else) with my late 2012 27 inch regarding random restarts.

Mine is less that a few month old and was fine and all of a sudden it would shut off on its own while I was away from my computer.

In my case, I found out why. Everything I sync up and plug my Running GPS(Suunto Ambit) watch to the iMac, it would completely shut off my computer. Not while i was on the computer but sometime during the day.

This thread is long which tells me that it's a common problem. I have several iMacs with the shut down problem. I was initially convinced it was the video problem. I removed the video card from a newer i3 iMac and within a hour I started both machines. The problem persisted and the i3 worked with the video card I thought was bad. It was not the video card. Nvidea had bad chips during that time due to the dye construction of the ball solder connections that attaches to the PCB. This was not the case. Logic tells me maybe the power supply is a issue, strike 2! The only thing left is the logic board or the LCD and driver board. I switched the LCD and the LED driver board just for kicks knowing it would not be the issue so therefore it's a logic board. I did not feel there is any reason to suspect the wireless, camera, 3 fans or DVD. I installed a new Hard Drive initially and different memory. That is the obvious. About six months ago I actually learned about a repair for a Mac Book Pro 2010 reset issue similar to the iMac through one of my clients who found a thread about a capacitor issue. He had asked me to replace the capacitor on the logic board for the reset. He even brought me the part which he purchased from Digital Key for $4-5. I took the old cap off and put on the new part. After many moths the problem did not change me back. It was once again a capacitor. Capacitors seem to be the number one problem in electronics. There is a bad capacitor on the main board and I am compelled to find it! By the way I discover my iMac will stay on for many hours if I let YouTube run videos. When nothing is running the computer shuts down suddenly and within 5 minutes. I think everyone is experiencing different intervals before a shutdown occurred which I find interesting.

Same issue. I have brought my iMac 5k in four times to Apple Authorized service centers.

here is a video of what happens.

https://youtu.be/3GfxM-C9c-I

How many trips is "Reasonable" before they replace it. I'm in California. There is a law on the books that says replacement is due after 'reasonable' attempts at repair have been made

Already replace graphics card and power supply

I can only restart if I unplug the power cord.

The issue was not present in the first 12 months. I have 5 months remaining on my extended warranty.

After 18 months of shutdown agony I was very frustrated. The local Apple Shop could never replicate the problem or find anything wrong with the computer.

In the middle of autumn here in southern Australia the problem became so bad that the computer was shutting down several times a day, including when it was asleep with no programs running or connection to the internet or to the Time Machine backup. It also used to sometimes die when I was shutting the machine down.

The straw that broke the camel's back was when it did that during a restart after a system update and corrupted the operating system so badly that Apple Support suggested I wipe the hard drive and reinstall the operating system from scratch. Even getting the existing information off the computer and onto a portable hard drive became a nightmare because the computer would abruptly shut down while I was doing it.

In desperation I decided to do what others have done and get the local Apple Shop to replace the power supply unit. Before replacing the power supply the local Apple Shop tested the computer again and still couldn't find anything wrong. One month later and I haven't had a shutdown.

If you are having this shutdown problem I would highly recommend that you try replacing the power supply first before spending money on replacing video cards, screens, CPUs etc.

You will probably have to insist that they do that first because they will still argue until the cows come home that it is likely to be one of the other components and not the power supply. Given how often replacing the power supply has solved people's shutdown problems shows that is not always true.

I have had the same problem! Mine is a late 2012, 27" iMac. It happened once in about January, then again around March, then twice in April, once during a recording session. Up until that time it had been great. I took to the Apple store- all hardware checked out, but they replaced the power supply and reinstalled the operating system (have been running 10.9.5 since it works with Protools 10 and the Waves Bundle I have doesn't work on Protools 11- I wanted to finish out some sessions before moving to 11).

Got different ram and I also replaced my power surge protector and got one that auto-regulated 120V. It was great for 2 months- thought it was fixed. Then it happened again- I was running nothing at the time. They replaced the logic board. Took it home and it hung in for 2 days. Ok- cut to the chase- everything was replaced, all factors isolated, 5th time to the "genius bar" and it is still not fixed. Yesterday I had them wipe it clean for the second time and I picked only certain applications from my time machine backup to put back on it. Brought it home and it stayed on for about 2 hours- then down again.

I finally said screw this- I'm losing money and ordered a new one.

I don't get why Apple can't find the issue. I'd at least like to be able to sell it and recoup some money toward the new one. They aren't cheap.

APPLE- WHAT'S UP????

Hi All,

I am back here after almost 2 years now. My 27" 2012 Imac was experiencing the problem discussed here. I left the system almost unusable for about a year, trying variety of experiment with in OS level and other soft were which I regularly using. I did nothing in the hardware department. Strangely for the last one year it works perfectly, not even a single shut down (unexpected) in my experience. I suspect the culprit is GTX 680 and it's drivers. I updated graphic driver along and OS to Sierra last year. I think this made the change to my system.

Regards

Rajiv

Howdy

I never did discover the cause or the solution. I suspected a heating issue, but then it would sometimes shut off when absolutely cold with no indication of any temperature rise from my monitoring utilities. It would definitely shut down when it overheated, which it would do when the graphics were pushed - gaming, Photos, even iTunes when scrolling through my hundreds of albums.

I could always count count on it to shut down when doing a file transfer from an external drive or a download from an online source.

I have read every thread I could find on the subject and most people have their theories. Every one of them has been acted on by someone and the fixes have failed - even total logic board replacements.

My solution was to wait for the new iMacs the past June and buy one. Ka-ching $$$.

Now my headache is being caused by the inability of the Migration Tool to see either Mac and my old Mac shutting down during manual file transfers. Yay.

If your old computer is still shutting down abruptly then its only future use is as a paper weight. So take your old computer to an Apple authorised service agent and pay them to remove the hard drive and put it into a case. Then you will be able to migrate your information to your new computer.

My iMac also shut down itself when I am using PhotoShop to edit photo, it happens for serval times after my iMac changed the power supply unit. After it shut down, it cannot open back at once. I need to unplug the electricity cable, and wait for about 5 minutes then plug it back, and the iMac can open again. I think I need to bring back my iMac to Apple support for repair.

The only answer that I am aware of is a complete break down of the entire computer and complete cleaning of every component. Then re-assemble and then the air can flow and won't over heat. It supposedly takes an entire day or more. Nothing needs o be replaced everything needs to come out be cleaned reinstalled to specification. But apple will never tell you that and they will never do it.

I am having the same problem that the screen just goes dark. Will not restart until I

unplug the computer from the electric source, wait about 10 minuets plug in the power cord

and then press the start button. the shut down can happen 3 or 4 times during the time I

am using the computer for say 2-3 hours.

how did your computer fare? I'm having similar issues - replaced HD and logic board. got my computer back yesterday, was running fine and lasted longer than before. It just shut down with a beeping noise and grey & blue vertical bars on the screen. Only option left is to replace the power supply...curious if that would fix it? My iMac is 2011 with OS 10.13.1.

I can't believe this is still happening after almost seven years without acknowledgement from Apple, 18 screens worth of discussion from over 1000 people. And they have been forced into 10s if not 100s of thousands in replacement parts under Apple Care and it is STILL a problem. Has anyone mapped out the actual machines this is happening to? Has it stopped after a certain model? Is anyone keeping a db of this issue?