On boot, iMac Apple logo blinks red after update to Mac OS Sierra

I get that the iMac needs maintenance, however I prefer it happens on my time, and not because Apple didn't fully test a O.S for all devices. For me it will take a lot longer then 2 hours, I use Ableton, Photoshop and Logic. All 3 will take awhile to install and 2 of the 3 are on disc.

Really?!?!? So let me get this right, I can re-install JUST EL Captain without removing any of my software on the computer (disc and downloaded)????

If so and if you don't mind, can you please give me a step by step what to do in saving some time by calling Apple and being on hold for an hour. Thanks in advance.

When I called Apple last night they were saying it would totally wipe my computer, meaning I'd lose all my disc software/downloads. Then I would have to undo licenses from nessessary software, then move all things not wanting to be lost to my external drive. So that's why I was flipping out on Apple, because I know to redo my iMac from scratch is a whole day lost, do to Apple's messed up new O.S

It won't, you can re-install it a billion times and you'll still end up with the same result, a flashing red logo along with a few other minor bugs ( Amazing work Apple :/ ). It seems to be effecting the late 2015 21" 4k iMacs. You are basically down to 2 options; leave it as is and deal with it until Apple, "maybe" comes out with a patch, or re-install EL Capitan. I'm trying to find out how to do this from someone else who left a comment, where he was saying it can be done without having to re-install all disc software and redownload from the app store.

I don't think you can roll it back to El Captain and I wouldn't try to do that. Just reinstall first and see what happens. It should work.

You can't talk to the support person that first answers the phone. They don't know anything! You need to demand they switch you over to a "senior adviser". The senior adviser knows a lot more about the process. There are several options to restore your computer. One of them wipes the whole thing clean. But there is another option on the list that doesn't wipe the thing clean. It re-installs the operating system without removing local files or programs that you installed. It was the senior adviser that recommended and walked me through the process.

Here is something I copied and pasted from the web. It sounds like the process I went through. If you choose "reinstall OS X" it won't delete any programs or content on your computer. It will say "should take 5 minutes" but it really takes 2 hours. Don't turn off your computer! Keep your mouse moving because the computer may go to sleep after 20 min. Then when it boots back up it will ask you some setup questions. You will think it wiped the computer but it didn't. Once you get back in everything will look the same as you left it. I would definitely talk to a senior adviser first to confirm before you do this so you don't make the wrong move. I would also tell him to walk you through the process of clearing your cache first. They had me delete about 5K files in a folder somewhere (i think the folder name was "cache"). A very simple process. Ever since I did this the computer has been very quick! No crashing. It feels like it did when I first bought in with El Captain a few months ago.

Boot up holding command-r keys into your Recovery Volume. First run Disk Utility > Repair Disk, if you get errors run until no errors reported or reports "the disk cannot be fixed". Then, choose Reinstall OS X. This will be an install "in place" and shouldn't effect any of your own data or settings.

That red box on the apple logo will NOT go away! That is a bug that will be fixed in a future release. Apple told me they were aware of it and working on a fix. It is just a cosmetic issue. But reinstalling OSX as I described will help with all of your other problems with regard to performance. Just talk to a senior adviser and tell him you don't want to wipe it clean from scratch. He should give you the same instructions that I just provided.

I have this same issue, too...

iMac (Retina 4K, 21.5-inch, Late 2015)

I've re-installed the OS after freshly downloading it...no change. Apart from this curious behaviour, I've not noticed any other problems. I've had a "chat"with Apple support and their suggestion was to do a Time Machine back-up, wipe the internal drive clean and re-install the OS. She also commented that there "may be a logic board problem" and I should take it into an Apple store. Sigh. In view of the distance I am from my nearest store and the fact I've not noticed any other issues, I'll wait to see what the next Sierra update does. However, I can't shake the feeling that it is warning of a problem...I recall very early Mac's would reset the date to Steve Job's birthday when the motherboard battery died...it's hard to believe that it's a "cosmetic issue"...time will tell.

I highly, highly, highly doubt it's a logic board problem, when there are a lot of other people experiencing the exact same issue upon updating to the new O.S. If you were the only case in questioning about the blinking red logo on boot screen, I'd say maybe you do have a issue with your IMac, but in this case I very much doubt it, as it would be very odd for all these people asking and commenting to have all failing logic boards all at the same time. I personally think bring your IMac into the Apple store would be a huge waste of time when others have commented, and said, when putting the O.S back to EL Capitan all works fine again. So either put it back to the old O.S or hold off to a possible update fix, seeing as a red blinking logo on boot screen is not actually effecting performance.

Paul... I have said this 3-5 times already and this is the last time I am going to say it.

The red box issue is NOT A HARDWARE ISSUE.

IT IS A SOFTWARE ISSUE THAT HAS BEEN CONFIRMED BY APPLE

AND IT WILL BE CORRECTED IN FUTURE UPDATES!

HANG TIGHT AND RELAX. The red box issue is ONLY COSMETIC. APPLE WILL FIX IT SOON!

The more and more I think about it, I think it's a bug with a resolution change upon boot, similar to a flashing screen when your in desktop and you get a brief flashing screen when/if changing resolution. Sierra is not specifically made for "only" 4k screens seeing that Apple does have alot of 1080p screens, so when the iMac is booting and has that loading bar with the Apple logo above I think it's having a resolution bug issue i.e. creating a red flashing logo.

Same problem and Apple Support acts as if they have never heard of it. Safe Restart did nothing. Reinstallation of system software did nothing. Have an Apple Store appointment, which I gather will also do nothing....

So you went back to El Capitan and are still getting the flashing red logo on boot, is that correct?? To the other person who commented to you, I don't care if they have a billion employees, regardless if they know how to fix things over the phone they should be on the up and up about things going on with their products, especially if your investing premium price. Like were talking if you've upgraded your mac it can be equivalent to buying a used car.

When this is the second time I've invested close to $3000 on an iMac since 2013, and it's had serious issues within 6 months and everyone is obvious at Apple you'll have to excuse my frustration. On my 2013 model when I took it in to the Apple store for servicing they ended up scratching my screen as an extra bonus, on another issue they never ended up resolving.

I have the same problem after the Sierra install: 1. On bootup red rectangle flashes behind Apple logo, progress bar flashes green. 2. On shutdown spinning gear is missing, 3. I worked with six different Advisors including several Senior Advisors. None said they were aware of the problem. We did all the trouble shooting previously discussed and none have fixed it. They all suggest it is hardware and I should take it in to Apple store.

Late-2015 21.5" iMac 4K retina display, Fusion drive

I'm going to call them tonight and speak to a Senior Advisor. If I hear anything but it's a software issue on there end, I'm going to hit the roof!!!!! I had a major problem with a 27" iMac back in 2014 where it ran into problems after only 6 months of ownership with only weekend use. Long story short Apple had my iMac in for service for nearly 3 months (no joke). After 2 months Apple finally decided to give a replacement unit, which came with a very noticeable chip in the glass (recorded the whole unboxing since I had already been through so much with them). So there solution was to send it to the Apple store again for glass replacement at another 2 weeks. On the first time bring it there it was scratched while in repair, so needless to say I was not impressed. During this time talked to more Senior Advisors then I can count, plus there customer relations (was the longest running open case from what I was told wother many applogies). Now this iMac at the same time of ownership (6 months) and as I said if I hear any, "I don't knows from them" or "bring it in for an appointment" or "it's a hardware issue" I truly feel sorry for the person on the other end as I've had it. (I don't drive neither so taxi will end up costing $40 per way just like I had to do with the 27").