OSX Update 10.11.3 Causes Grey Screen of Death Mid 2011 iMacs

Hello everybody,

I'm new to apple forums, so I'm not exactly sure if this is going to make it to the right place. This isn't as much of as question as it is a PSA.

Basically a summary of my post is OSX Update 10.11.3 causes both 27" & 21.5" Mid 2011 iMacs to no longer startup properly. After the update installs and your iMac restarts, the boot sequence looks just fine, showing the Apple logo and then progress bar. However, when you're expecting your login screen to appear, instead you are greeted with a dark grey screen and movable mouse cursor...and that's it. The system is still somewhat responsive. If you hit buttons on the keyboard you hear the "bum" sound as if you were to press a key when you weren't supposed to, and if you press the power button (not hold it) the system goes to sleep (and wakes up if you press it again). So it's not really frozen, it's just kind of...there.

Stumped, I went to Google, hoping to find someone with a similar problem. I didn't find much. I found some people with similar problems (grey screen is a little bit general), but I did find other people with 27" mid 2011 iMacs have this issue (links below:)

Unable to install El Capitan Update 10.11.3 (Stuck in grey screen)

iMac mid 2011, gray screen of death!

gray screen with pointer at login screen

From what I've read, certain iMacs were recalled for graphics card failures, and that's what some people responded to in the posts as a possible cause. (This also is what mainly comes back when you search "27" iMac grey screen) But this doesn't seem to be the issue here. The above posts are fairly recent, and seem to coincide with update 10.11.3 being rolled out, and they are the same symptoms as I'm experiencing, but with no working solutions.

Once I restore to my last time machine backup before update 10.11.3 is installed, the system works flawlessly. Sadly, if you don't have a time machine backup to restore to, it seems reinstalling OSX is your only solution (until you install the update again)

I'm by no means an OSX expert, but I have tried everything under the sun to try to get the system to boot up properly again, like PRAM & SMC reset, single user mode, safe mode, none of this works. The system just won't boot.

I don't know if this has affected everybody with mid 2011 iMacs, but I just thought I'd let people with 2011 iMacs that are having trouble with this update that you are not alone, and I hope someone at apple can see this. If you have a 2011 iMac that hasn't been updated to 10.11.3 yet, I would refrain from doing so.

Thanks

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