OK. So here I am, 8 or so months after this problem initially began (Feb 2012), and still this problem continues. After Apple replaced my HD, the problem continued that week. I contacted Apple Care and took the computer into a different Apple store. They kept it over night and ran more tests, and weren't able to find anything wrong. So the Genius tried a fresh install of Mountain Lion (for free) and iLife '11 (for free), however during the installation, the computer shut down! So now that he's stumped, he adds a whole slew of notes into the system and keeps the iMac for a few days. They replace the power supply, processor (Logic Board 2.93GHz Intel Core i7), video card, and audio cable. All covered by Apple Care thank God. Reinstalled Mt Lion, iLife 11, and integrated my previous info from my last backup. At this point I'm relieved!
Later that week. My computer shuts down twice. And has done so another few times while using it. I haven't contacted Apple yet. I'm just frustrated and upset and too busy to take it back in and wait for them to try and figure it out. The problem could really stem from the 16G of RAM I installed post purchase, but according to Apple, they ran tests on the RAM and found it to be OK. Soooo yeah.
8 months, and still no resolution. They pretty much gave me a new 27in iMac! And yet I still have this issue.
To be continued...
I've been having the same problem for a couple of years now. 27-inch iMac running 10.6.8. I added a hard drive, though, through OWC, so figured I had no recourse with Apple. Mostly it shuts down when I'm running Facebook, especially if I scroll. Can't scroll! No scrolling! Or if I try to work on a large Photoshop file. Very unsettling, frustrating. Did you ever find any kind of resolution?
You don't say how much RAM you have installed or if you added any aftermarket RAM. It might be intermitent RAM problem. This could be caused by overheating if the fan or heatsink is full of dust of if the fan bearings are getting a bit "sticky". It may also be, since you are running 10.6, which is a bit older, that you are maxing out the RAM and forcing a lot of disk activity to act, sort of, like additional RAM. Use Activity Monitor to see how your page ins and outs are looking.
You may want to download and install the iStat Pro widget to monitor RAM use, several internal tempratures and a number of other things. You can get it at:
Here is a bit of info on Activity Monitor:
I have 16 megs of RAM, no aftermarket RAM, a dedicated SSD for the system and applications, a 2-terabyte drive for internal storage. No overheating is occurring as far as I can tell. The shut-downs happen mostly on facebook for some reason, and always when nothing else is running or open. They happen unpredictably but I can almost guarantee that they will happen if I scroll on facebook or click through too many times on facebook. Often within moments of opening facebook and starting up the computer.
Also happens when I view certain weather maps and try to animate them. And can occasionally occur if I try to open a large photoshop file.
16 MEGs??? Judging from the way the rest of the computer is stocked, I think you mean 16 Gigs.
Does the Facebook shutdown occur with any browser (Firefox, Chrome, Safari, other?) or just one particular browser? Same for weather maps. The only thing that seems to indicate it is not a browser issue is that you also get a shutdown, but only ocassionaly when openig a large Photoshop file.
Also, just curious, with the high level of resources, you have invested in the computer, is there some particular reason you are staying at 10.6.8? I wonder if the problem would happen with 10.8. That is only a thought and not a suggesdtion to go to Mt. Lion. Are the other Apple updates (non OS) all current for your system? I mean things like firmware updates, Java updates, security updates, etc.?
Have you tried eliminating all the plugins and extensions for your browser(s)? Just wondering if there is some conflict taking place. Also, is your browser fully up-to-date?
Does the shutdown happen when you are running a bare bones configuration? I mean with no printers, connected, no scanners, USB flash drives, or anything other than just a wired keyboard and wired mouse connected to your USB, Firewire or video ports. Reason I ask is if there are a things connected is I wonder if they might be putting an additional load on the power supply to where, when it is called to really pump out the power for the more demanding applications the power supply kind of chokes out.
Yikes, yes, thanks, I meant Gigs.
It happens ever so slightly more with Firefox than with Chrome. But it happens in both. I don't use Safari if I can help it.
I have a Wacom tablet and an Epson 10,000 scanner attached via USB. And a little HP deskjet printer. I have tried unplugging them... makes no difference.
I am up to date on everything... just haven't wanted to migrate to 10.8 because this is my home computer, which I use in my home studio, and it has to be the same system as I use at work on my PowerMac. Everything is working so well on the tower that I don't want to update just now. If it ain't broke, etc. But I do like to take work home and work on it there at times and lately the iMac just won't do it. Used to, at first. Always been shutting down with facebook, but the shutdowns with photoshop are recent.
Come to think of it, I haven't tried unplugging the scanner. Will try that.
I have not tried working with a wired mouse and keyboard! Great suggestion. I will try that in the next few days if I can and report back.
Nope, no solution! I tried everything. The problem seems to come and go with facebook. It isn't shutting down as much with facebook as it used to. Now the major problem is that I can't open a large photoshop file. Down it goes, immediately. Nothing seems to make any difference except perhaps the phases of the moon. I am, however, knock wood, able to restart immediately. You have my sympathy.
If it takes many hours to reset itself, it might be a power supply that has a problem and is dying due to overheating. Normally just unplugging the computer for five minutes or so is adequate to reset the SMC. That is the micro program that controls a number of things during the boot up process. It may also be a RAM stick overheating but I would not think that it would not take several hours to cool down.
Have you tried pulling out one pair of the RAM to see if the problem changes. If you have four 4 Gig sticks, try pulling out he top pair and replace it with the bottom pair. Then try the replacing the pair that is in with the pair you pulled out. It just might be possible that you have an intermitent RAM problem. Your system should run with 8 Gig installed but it might be a bit slower.
Also does it still lockup when you are running in Safe Mode (hold shift key when powering up)? Also is the activity monitor showing anything running that you do not expect pr even know about?
Well, I left it unplugged overnight and tried it this morning when I came in...I get the chime, grey screen, then it dies before the Apple logo shows. So appears no amount of unplugging is causing it to boot. I agree that it is looking like the power supply. I am going to setup a genius bar appointment to confirm and get an estimate on cost to replace power supply. I had 4 sticks of RAM in it, the 2 original, plus 2 extra ADATA chips. I have tried both sets independently with no difference in the operation of the machine.
I have been reading all these posts and I must say I have been jumping up and down in frustration!
Your problem which you are saying is definitely a power problem and the power pack in your iMac needs to be taken to the apple store and a replacement fitted. If you like in the uk that will cost you around £80. Or $120 or there abouts.
Please book an appointment at the Genius Bar.
I, too, have been plagued by the unexpected, random shutdowns I've experienced since July 2013 (after my computer was opened up for repairs). I have a 27" iMac, late 2010, 2.93 ghz i7 quad, 16 gb ram, on 10.6.8.
I had no problems with the computer, which is basically an image workstation, until July 2013 when I noticed slowing performance. I took it to the Apple store in Houston, and they diagnosed it as bad logic board, which had fried 1/2 of my ram. I had the board replaced, and a few weeks later, the shutdowns started. At first, they were spaced apart far enough that I wasn't losing much work. Later, they were more frequent and frustrating, so I took the iMac back to Apple and left it there for 3 days for diagnostics. I was told that the hard disk was showing errors, so I had that replaced at my expense. Apple also replaced the logic board again at their expense. Same result - a few weeks later, the shutdowns began again. Normally, these occur when the computer is awake, and I normally have LightRoom and Photoshop open, and Safari. Sometimes a lot of data is being crunched, and other times the unit is not under demanding processes.
I avoided taking the unit back to Apple during the holiday madness, so I went back in January 2014. One of the geniuses thoroughly went over my use of the computer as he ran tests. We looked at the Console, and he had some suspicions about connected peripherals, especially my Wacom tablet. Apple agreed to replace the video card, and I picked up the unit about 10 days ago.
I unplugged the Wacom after the last repair, and had a shutdown on 1/31. I reloaded the latest Wacom driver, but had a shutdown 02/08, and it still was unplugged. I unplugged all USB items except my mouse, and had a shutdown 02/09. Only my Burly tower with external drives is connected by FW800. A older Cinema 23" is connected for my palette monitor.
I've checked the power cord, and other items plugged into the UPS do not falter when the iMac shuts down.
If my understanding is correct, if it were to be a power supply problem, I could not re-boot after a shutdown. I can re-boot immediately.
I've lost so much productive time with this iMac and the time and money lost while it is at the Apple store.
Latest update: the Apple Store called me 48 hours later and said they just think that it was a loose connector on the display. Doesn't make a whole lot of sense to me, but I said ok and went to pick it up, at no charge. Since then, I have brought it home and it has been on ever since, hasn't shutdown once...but I am keeping a close eye on it. Will update in a week or two and let everyone know if I am still having any problems. I asked for more details on the disconnected "connector" but they didn't really have any.
Hello. I have a iMac OS X 10.7.5 and it keeps shutting down randomly by itself. It started doing this in january 2014 and i don't know what is causeing it. I took it to the mac store and they ran a complete assesment on it. about 2 weeks later they called back and said that they couldn't find anything wrong with it. Note that since they did not take in my computer to "my" power cable that i was useing "I assumbed" it was the power cable itself, so i got a brand new one. My computer wasn't turning off as much then but i wasn't using it as much ether. but now it is back to shutting down back itself more frequently again.
When I took it into apple they said they never saw it shut down by itself and that they found absotulty nothing with with my RAM, logicboard, screen, Nothing.
I'm checking to see if there is something wrong with the circit breaker in my house but nothing else seem to loose even a few seconds of power.
I write this out of fear of my mac shutting down again, so forgive be if im blunt and have bad spelling or grammer