Late 2012 (27") (i5) iMac - Keeps shutting down!

Firebrandnire wrote:

... I do know that I had installed an app called Memory cleaner around the time the iMac started playing up,

Get rid of it.

Excerpted from Effective defenses against malware and other threats:

Never install any product that claims to "clean up", "speed up", "optimize", "boost" or "accelerate" your Mac; to "wash" it, "tune" it, or to make it "shiny". Those claims are absurd.

• Such products are very aggressively marketed. They are all scams.
• They generally operate on the flawed premise that a Mac accumulates "junk" that needs to be routinely "cleaned out" for optimum performance.
• Trial versions of those programs are successful because they provide the instant gratification of greater free disk space.
• That increased space is the result of irreversible destruction of files, programs, or operating system components normally protected from inadvertent alteration or deletion. The eventual result will be unreliable operation, poor performance and random crashes that may not become evident for months or even years after their use, when updates to programs or OS X are eventually released.
• Memory "cleaners" that circumvent OS X's memory management algorithms work by purging inactive memory contents to mass storage, which can only result in degraded performance and accelerated hardware failure.

Apple Hardware Test is of limited use and won't help at all if the problem is intermittent. The best it can do is identify obviously inoperative hardware.

Do you recon the Memory Cleaner app may be a possible cause to the problems I've encountered?

Not really, but as I wrote such things cannot possibly convey any benefit, will only result in degraded performance, and can certainly contribute to or accelerate inevitable hardware failure. Its presence is a distraction that will complicate troubleshooting.

OS X's memory management differs in fundamental ways from Windows. Apple's proprietary algorithms are considerably more advanced, so some of that article's recommendations are not applicable to OS X. "Worse than useless" is an accurate description though, including categorizing PC "cleaning" apps as scams. This is exactly what I have been saying. The undeniable popularity of such garbage attests to the gullibility of consumers.

I'm been having exactly the same issue for the last 6-9 months.

Gave it to Apple for a week and they monitored it for 24hrs (even though I said sometimes it doesn't switch off for days and sometimes it'll switch off 3 times in an afternoon). They came back with 'no fault found'.

I also had a memory cleaner app, but I removed that App months ago and the issue is still happening.

I have wondered if it's an issue with the power supply to the property and the iMac being susceptible to minor fluctuations that may be present. (It acts the same in all power sockets). I plan to take it to work and try it there to rule out the power supply, or try and borrow a UPS.

It's strange that it does seem to be the same issue with a particular model that a lot of people are experiencing.

having had the same problem as listed by so many users, `I have also tried many methods to try and stop my iMac shutting down. So far, the best method I have used is to start the iMac in the usual way. As soon as the starting sound is heard I press button and back and close down and then start up immediately again. The shutting down does not happen again on that day. I have been doing this for a few weeks and so far, so good

Yeah I have the same problem with the same model. So bloody frustrating. Tried all of the things mentioned above. Anyone find a solution yet? Cheers

Open up as usual then immediately force close with button at back.... then open up again. My iMac has stopped shutting down with this start-stop-start method.......so far!

At which stage of the start up? You mention above to do it straight after the start up sound. But are you now letting it start up until you sign in and at your desktop picture? Then hold the power button? Cheers

Start up by pressing button at back - wait for sound - close down - wait about 10 secs. and start up again and run normally. As I said it works for me.

I took mine to the Apple Store and they formatted the drive, reinstalled the OS, then I restored from Time Capsule and it has taken care of my issue so far.

Before this I had about 7 random shut offs per day. Apple Store employee thought there was a problem with the OS kernel.

I've been having the same problem as everyone else on this discussion and it is frustrating and can not understand why Apple can not identify the root cause or put out a communication on this. I took mine to Apple store, you did a full hardware diagnostic test, re-formatted/re-imaged the disks, and then reinstalled OS El Capitan (since then I've loaded Sierra, and still having problem). Restored all my data from backup. Problem went away for about 5 days, and then reappeared. Now it seems to be happening quite often, and the only way is to pull the plug, wait 2 minutes and then plug in and restart. Sometimes it crashes right away. Very frustrating.

Sad to report that after about 8 days of running fine, the problem reappeared. Even when I reformatted and put on Sierra and before I restored via Time Capsule... seems to point to hardware issue. Would love a fix, interesting that I am not alone.

As many of you who are experiencing this issue already know, there are a lot of other iMac owners who have the exact same problem, with NO known solution. Somebody at (imacshutdown at gmail) is compiling a list of users whose iMac computers are unexpectedly shutting down, and I'm hoping they're able to get Apple to act. For many of us, these computers are essential to our livelihoods. We're professionals, and these are the tools of our trades. We made a large investment when we purchased these machines, and they just do not function. A lot of us have been unable to finish the jobs we were hired to do, because our computers shut down in the middle of a project. We're losing our clients, and we're tarnishing our reputations.

Have had the same problem with a 2015 27" iMac. It has been rebuilt twice and had its motherboard replaced. Worked fine for 2 days and now will only stay on for 5 minutes. I have not reloaded any of my old programmes in case I had some glitch in them so basically just put my iCloud files on. Won't even start from a restart At the moment. Getting really frustrated. Seriously considering having to buy another but then worried the same thing will happen. On off trick it has at least started up without having to disconnect power.however crashed again after five minutes.