iMac shuts down randomly for no apparent reason

It is simply not possible to determine all the effects that can result from having used MacKeeper of any other similarly categorized "cleaning" utility. For Macs that have been affected by their use, the only action I can comfortably recommend is to erase the Mac completely. It's what I do after evaluating them in an effort to diagnose other people's Mac problems.

If — and only if — they were merely installed and not actually used, uninstalling them is simple. It sounds as though you actually used MacKeeper though.

I'd still be surprised if MacKeeper is cause of the random shutdowns.

A few weeks ago my iMac (27-inch, Late 2012) started to not wake up from sleep in the morning. The only way to re-start it was with a SMC reset. Then it started blacking out randomly during the day and also would only restart with a SMC reset.

To see if I could identify the conditions that would trigger a blackout, I installed the "System Monitor" app from the App Store and started monitoring the temperature, fan speed, and cpu load, as I used the computer throughout the day. The random blackout continued and I could not find any correlation between temperature, cpu load, or fan speed, and the blackouts.

After one of the blackouts I re-started the iMac holding down the D key in the keyboard to boot into Apple Diagnostics. The quick test did not find any problems, but when I selected the extended test, it seemed stuck at 34 minutes during the pass 1 of the memory check, even though it was running for more than 2 hours. I tried stopping the test but it did not respond to the mouse or keyboard. As it did not respond to the power on button, I pulled the plug.

I pulled out the 8 GB memory upgrade I had installed about 2 years ago and left only the original 8 GB from Apple. I rebooted into Apple Diagnostics again and this time the extended test completed in less than one hour and found no errors.

At least in my case, it seems that the problem was caused by bad memory. Now, with only the original 8 GB that came with the iMac, it has been working as expected for more than 2 days. The display brightness is set to automatically adjust, and the computer sleep and display sleep functions have been working as expected.

I had a similar problem with my iMac. Some time ago, I added two 4GB memory sticks, purchased from an on-line vender. After Apple Support and I had tried everything else, I bought two new memory sticks and replaced the ones that I had purchased earlier. Problem solved. Apparently, there was some sort of minor malfunction in one of the memory sticks that caused the periodic shutdowns.

In my case, I have not added any RAM to the factory installed 16 GB (2 x 8). And, the black screen/unresponsiveness is mostly when I have anything attached to USB ports 1 and/or 2 (from left). The Capture Data files were uploaded to Apple, so I will see what their Engineers determine (if anything); because of the holiday and the fact that most of them are off this week, I don't expect anything before early/mid next week.

Please let me know what they decide to do. Even if you had to pay for a power supply replacement you'll be doing something.

... buying a new HP PC

Good luck. The last HP I owned literally spent more time in the repair shop than I had it for my own use, until its warranty mercifully expired and I threw it in the trash.

As for their user support forum, judge for yourself: http://h30434.www3.hp.com/t5/Laptop-and-Notebook-Computers/ct-p/Notebook. You'll find a lot more users giving up on them and moving to Macs than you will find users on this site going the other way. Enjoy.

So, I am joining this thread with similar problems. The random shut downs started 5 days ago. iMac (27-inch, Late 2012) recently was upgraded with Crucial memory and the last couple of days I have been reading many articles on "memory upgrades" causing shut downs. Fortunately, I have the original 8GB Apple memory, but the shut downs are persisting.

I wonder if we are all subject to Apple planned obsolescence?

Now, one outstanding wildcard is the 3TB Fusion Drive recall. I have not had that done yet, so maybe it's time I give that a try.

Thanks to John for all the help re. error codes in the system console. I am also a case of error code 5:

Same issue here, started 2 months ago and I tried to wipe the HDD and start all over again. And am using a new powercord.

I guess the power supply is probably at fault, and I can only hope that Apple will acknowledge that there is a problem here.

iMac 27", late 2012, i5 3.2 GHz, GeForce 680MX 2GB, bought in Denmark.

Yup. I've tried reconfiguring the RAM, wiping HDD, reinstalling OS X, forcing my fan to cool things down. Very frustrated, and for the first time in two decades I actually don't think I want another Mac after this.

Mike have you got your problem sorted out?

I have the exact same machine with the exact same problem (Late 2012, 27 inches, i7 3.4GHz, 3TB Fusion, 680MX, 32GB of original Apple RAM)

I also had a history of acidental cord pulling but I thougt it was because of the 3TB which I got replaced.

If you got it solved by replacing the power supply please let us know so that I'll save myself extensive trips to Apple Store.

I have the same problem. Same Computer with 32 GB Ram. I have taken it in to Apple, who states that it never shuts down for them. I had all RAM replaced, I had motherboard replaced. Just shut down again, I am posting this on my PC. I have taken it in four times, and they claim no problem. Every time it shuts down. Also I get an out of memory error as well that no one can explain.

This may not apply here, but I had a problem with my iMac not waking up (and silently/in the background shutting down) whenever a) I had one of my external hard drives plugged in and b) allowed it to go to sleep. When I wanted to wake it, it would not work - it was dead and the power button did not work (nothing else did either). I had to unplug/plug it back in. This only happened when I had a hard drive attached. It was finally determined that Apple made a change in the OS late last year which resulted in the malfunctioning of the external enclosure's chipset (plug). Once I got new hard drives with different chipsets (OWC replaced them as they were still under warranty and they were working with Apple to get a handle on the problem), I haven't had a problem since.

I've been having the exact same issue with the exact same model of computer. It's been at the Apple store at least 5 times over the past two years, and after escalating my case for months they replaced my logic board and power supply. The machine still shuts down without warning. I'm absolutely livid.

This has happened to me for more than a year. It's been into the Apple shop for a total of 3 weeks on two different occasions, and they just say it's power. I did all the things you have outlined too, and it is still happening. Completely infuriating and an extremely expensive paperweight. I'm livid that Apple hasn't thought to check the logic board as is explained in this thread. I'm giving it one more shot and then giving up.