Model A1312 / Mid 2011 / 2.7 & 3.1 GHz Core i5 or 3.4 GHz Core i7 Processor, ID iMac12,2

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Suggestions to fix white screen when booting

My 27" iMac from 2011 (bought with dual drive: SSD & HDD) won't boot anymore, I'm getting the white screen. When I turn on the mac I hear the startup sound. I'm getting the Apple logo and see the loader. When the loading bar is at about half I'm getting the white screen and my Mac stays unresponsive.

Tried the following:

  • Reset NVRAM/PRAM: Could not manage to do this. When I pressed the keys after some time I got the firmware lock / login screen. When I put in my password I was getting a white screen as well.
  • Reset SMC: Removed power cable for a night, put power cable back in, powered on Mac, nothing happend.
  • Boot in verbose / single user mode: Also unable to boot in verbose / single user mode, when pressing the keys, nothing happens, just boots until logo, loader and then white screen
  • Removed RAM: Booted without RAM, Mac gave the 5-second interval beeps. Replaced RAM, again logo, loader, white screen.
  • Pressed Option key to select boot disk, does not matter if I select normal disk or rescue disk, both same result.
  • Tried to boot to Windows (had BOOTCAMP setup) using Option key and for Windows I got a similar result: I saw the Windows logo + loader, then black screen and could not boot any further
  • Replaced SSD drive with new SSD, same result
  • Tried to re-install, created bootable USB. When booting from USB, same result, logo, loader and then white screen.

Does someone have some suggestions as to what else I can do? Any suggestions as to what might be broken?

Answered! View the answer I have this problem too

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A white screen is indicative of a bad hard drive. In your case it sounds like you have a fusion drive set up so it's harder to diagnose. Since you have a bootable USB device, I would start with it. Disconnect the hard drive and remove the SSD. Now see if you can boot just from the stick. If so, then install the most likely failure candidate, the hard drive and attempt a repair using Disk Utilities from the USB. Even better would be to put the suspect drive in an external enclosure.

UPDATE 8/7/17

I would really feel better about this if I knew for a certainty that that USB flash drive would completely boot on another Mac. (Then try it on the iMac with both internal drives out. That said, I've done reflows on the GPUs on this machine and the 21.5" with about a 70% success rate. You don't need a high end hot air work station to get the job done. iFixit does not have a guide for the 27" but does for the 21.5" and the are going to be almost identical when it comes to the card. Here is that guide, if you decide to do the flow let me know and I'll recommend an economical hot air gun. iMac Intel 21.5" EMC 2428 GPU Card Replacement

The video card for your 27" machine is Apple Part # iMac & 661-5969-R

The part is not cheap. I'd like to see you try a reflow of the card before buying the card. An inexpensive station is about $100 and after use you could resell it for 3/4 of what you paid for it.

What have you got to loose?

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Yes, I also thought it was the disk, tried a couple of things, but unfortunately that did not fix it. It is a separate SDD and harddrive (no fusion, 2 disks, SSD is installed below CD drive). Disconnected the disks but was still not able to boot from the USB (same issue, Apple logo, loading bar until half way then white screen). Could read all my files from the SSD from an external enclosed. Although I could read the files I still replaced the SSD with a new one but kept the same problem. I'm a bit out of ideas now...


I'd still go after the drives. First see if that USB drive will boot another Mac. Did you attempt a system update just prior to it failing? How far is the progress bar getting? Have you tried Safe Mode?


The USB is bootable. Did not execute a system update. The progress bar is about half way when the screen goes white and unresponsive. When booting in Safe Mode I'm getting the same result, the system boots to Apple logo, then shows the loader but when the loader is half way it freezes again.


Usually the system hits the video driver at about 55-60%.


Thanks so much for helping out. From what I'm seeing (loader until about half way) it could be the video card that is broken. Are there things I can try to make sure it's the video card? Is is possible to replace the video card? My Mac shipped with AMD Radeon HD 6970M with 2 GB GDDR5.


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Have the same problem as above with my 27” 2011 iMac. Tried everything. If yhe problem is the Video Display Card, would the Apple Hardware Test confirm it?

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I have the same issue (27" 2011 iMac). Apple Hardware Test does not show a problem.


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I just solved this issue!!!

The problem is, I've no idea how.

I've bought a second graphic card on eBay, but even with the 'new' graphic card the problem was exactly the same.

So I've unmount the motherboard again and again.

I've removed the battery of the motherboard for a few hours.

I've tried the 'old' graphic card without cooler: I just plugged it into the slot (without cooler) and without unmounting the motherboard.. and bingo.. the iMac start working again. I've really no idea why.

Block Image

I plugged the graphic card 'the hard way' without a view on the slot.

May be it has moved a pin or something ... I really don't know.

I was able to remount everything correctly, with cooler and all cables, and the iMac is working again.

That's a mystery.

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Geert will be eternally grateful.
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