iMac Intel 27インチ EMC 2309 (Late 2009, Core 2 Duo 3.06もしくは3.33 GHz) ID iMac10,1, EMC 2374 (Late 2009, Core i5 2.66 GHzもしくは Core i7 2.8 GHz) ID iMac11,1

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Why does my iMac shutdown halfway through loading on startup?

I get a chime then the Apple logo appears, then the progress bar gets to about halfway, then it shuts down.


  • Late 2009 27" iMac Intel Core Duo 3.06ghz
  • 128GB Samsung SSD installed in place of Optical Drive.
  • Stock 1TB HD
  • 12GB RAM, 2x4GB and 2x2GB. The 2x2GB sticks are the stock RAM.
  • OSX Yosemite.

Background Info

  • I haven't used the iMac in about a month as I have a Macbook Pro from work that I use primarily.
  • I turned on the iMac yesterday and the Startup was VERY SLOW, like 5 minutes.
  • I looked at some forums and saw that I should make my SSD my primary boot drive. I did this and restarted but the boot time was the same.
  • Next I shutdown the computer and restarted the SMC. This made the boot time a little bit faster, maybe 2 minutes but it still wasn't acceptable.
  • Next I reset the NVRAM 3x and this made a significant improvement. It was now at about 25 seconds.
  • When I finally logged in I opened up Photoshop and Firefox and they both just bounced on the task bar for about 2 minutes. Photoshop finally opened but Mozilla did not. I looked in the Activity Monitor and I kept getting CrashReports that were taking up 75% of the system.
  • I did some googling and it seemed like I needed to run First Aid on the SSD.
  • I went to Disk Utility and tried Verifying the Disk and it gave me an error saying that it could not be verified and that I would need to open it up in Recovery Mode.
  • I restarted the computer and held down CMD+R and nothing happened, it just stayed on the white screen. I held down the power button until it shutdown and the powered it back up holding option. It showed that I did not have a recovery partition (even though I remember having one in the past). It did show my Samsung Drive.
  • I clicked on the Samsung Partition and it loaded about halfway then shutdown.
  • I tried just starting the computer up normally without holding anything down and it would do the same thing.
  • I decided that I didn't have anything on the computer that I desperately needed so I was just going to reinstall Yosemite.
  • I downloaded Yosemite on my MBP and made a bootable USB drive for it. (This took about 4 hours).
  • I went back to my iMac and plugged the USB drive in, turned on the iMac, and held down option (expecting that it would give me the option to boot from the USB Yosemite Installer) and it chimed, the apple logo came on, the loading bar got to halfway, and it shutdown.
  • I tried this about 5 times and it did the same thing.
  • I tried resetting the NVRAM and it just shuts down.
  • I've tried Safe Mode, resetting the SMC, option, etc. Nothing works.
  • I left it unplugged over night and tried starting up this morning and I get the same thing.
  • Yesterday I took out the 2x4GB ram sticks and made sure the stock 2x2GB sticks were properly seated. I tried resetting the NVRAM and it still loads halfway and then shuts down.

I don't know what else to try. When I used it more often a couple of months ago it was very fast upon start up and running memory intensive programs like Reason, Autodesk Inventor, Parallels, Ableton Live, etc.

I am very comfortable taking the computer apart I just don't know what to look for.

Thanks for the help,


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I have the same problem, my imac would start halfway and it shutsdown. I was looking at the comments here and I am sorry because I am not much of a computer wizard:(, can you please teach me if ever, step by step on how to fix my computer please please please


Exact same problem with iMac early 2009 model.


My 2011 27" has the same problem, it will load halfway the shutdown. Was working fine yesturday, now it doesnt. Ive tried starting it up and holding alt or options (i have a windows keyboard) and that didnt work.


well, my iMac purchased in 2010 is doing the same thing. there are just a couple of documents I'd like to get off of it without spending a lot of money. I can't understand the solution at all. Not computer savvy.


Last week I faced a similar іѕѕuе, my iMac was shutting down halfway through loading on startup

I tried I tried everything and nothing worked.

Finally I managed tо fix this problem after getting help from Apple Mac Support

Follow the steps here:

It should solve the issue



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I suspect your logic board is shutting down from a thermal event.

Have you tried booting it up in Target mode and then connecting it to your MacBook Pro see if you can access the SSD and HD that way?

If you can see If you can install this on it: Temperature Gauge Pro. What you'll need to do is first down load and copy over to your HD on your iMac the installer file. Then reboot your MacBook Pro so it boots up under the iMac's SSD or HD (which ever you have as the boot drive). Then run the installer.

Once installed you should be able to reboot your iMac and let is capture what the thermal sensors are telling you. You will likely need to buy the full version to get the logging function to you can then review it again in target mode with your MacBook Pro.


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I finally got my Firewire Cable from monoprice.

I connected my iMac to my MBP and turned on the iMac and held down T.

I finally got it to boot into to Target Disk Mode after about 5 tries.

I was able to erase my boot disk in disk utility and install Yosemite back on to it.

My iMac now boots up in about 10 seconds and is running great.

I will install Temperature Gauge Pro to monitor and hopefully prevent any future issues.

Thank you so much for the help!


Happy it worked out. So the bottom-line here is the OS was not properly installed for some reason and using Target mode made the difference. I'll need to remember that one next time.


I have the imac27 and i'm experiencing the same problem. imac27 powers off in the middle of the boot up process :0( We're you ever able to get your imac up and running again. I do get a thunder bolt passing around my screen when I held T down.


Hello K Lin and Dan, I think I have the same problem


Thanks Dan! I figured a thermal issue as well. In LA and it's hot! Also since classes started last week I haven't put it to sleep or shut the system down in 4 days.

I can hear the fan inside at the rear but it sounds weak.

Again thanks for the knowledge

Cory Stewart


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Hi! I had the same shut down while startup problem. Restarted the Imac 24 (2008), holding the command+R buttons after the startup theme until some soultion options came up. One option was to restore from time machine backup. I did not have time machine turned on on this machine, so I got my macbook pro and an external HDD, made a time machine backup. When that was done, I plugged the HDD into the Imac, which recognized the system backup of the macbook pro, erased the old "broken" OSX along with the whole Mac HD, and installed all the system from the macbook pro (including softwares, browsing data etc.). After that it restarts itself and works happily. Always have an external HDD connected to your mac and have time machine turned on! It gives you great safety.


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Good logical thinking ;-)


Hello Eric, how do you transfer all of your system and software from your macbook pro to your Imac? My imac has the osx el capitan and i think out macbook has the maverick, how do you create a time machine back up? Can you please help me out? Do i need thunderbolt cables? Im frustrated coz im not good fixing computer problems. Thank you.

Edwin S.



Actually I don't mind that this is an old case file,

It contains so much worthy data that can't always be duplicated.

If anything,, it should be a tag added to new case, for reference.


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I have this same problem and I can get the iMac to boot to the Target Disk mode. Once there, however, I'm stumped as to how to reinstall Yosemite. I have no install disks and did the original update through the App Store.


Thank you,



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@Kenny, you'll need a second Mac to connect to yours. Basically your Mac is a very large external drive to your friends Mac :-}


Hi Dan,

Thanks for the reply.

I have a MacBook Pro that I can use. I've been trying to move files from the hard drive on the iMac, in Target mode, over to the MBPro. Then I saw this thread.

So, I think I have the items needed but I don't understand the steps to go through. Would you be able to help me out with that list?

Thank you!



Not sure I follow you here... So you have the two systems hooked up via FireWire, Thunderbolt or Ethernet cable, and the MacBook Pro is accessing the iMac's hard drive, correct? It will be an external looking disk on the far top right of your desktop (as long as you don't have any app.doc icons sitting there). You may need to go directly to it from the menus. go to Go then Computer which will open a fresh window. Using the twisty you should be able to access your iMac's HD.



Can anyone YouTube these steps or send the link for one? I'm computer illiterate :(


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Lisa Gill this question is a bit old and may no longer be visited by a lot of people that answered. I'd strongly suggest that you ask your own question and see if @danj can help you with that.


I think it would be more than one video, because diverse steps are described.

But actually, the steps are written, as long you can read you would be able ;)

Maybe also googling what the expressions mean: the first solution talks about Target DiskMode, the first comment to that talks about holding the T-key. So that is the key to activate your hard disk as a mere "target" for another computer, the way to connect it has to be googled (it depends your hardware)

Recovery Mode = holding the R-key helps you yo get to a basic recovery menu, google the options

SMC & NVRAM reset = resets preconfigurations of your computer (basic things it does when starting), I always google it , because I forget the keys for it.




K Lin さん、ありがとうございました!

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