Late 2015 5K iMac does not boot

[nitropowered]

So I'm supposed to be selling my 5k iMac and I was in the process of wiping and reinstalling high sierra. However, I reformatted the drive and well now its completely buggered. I can boot into recovery mode but when the bar fills up, I just get a there was an error and have to restart screen.

I tired making a recovery usb and it boots fine but when I click install high sierra it does the same thing and restarts. I'm pretty sure it has something to do with the fusion drive.

I'm really stuck and need to try to get this fixed asap!

Any help?

 

[Brookzy]

Personally I would split and then recreate the Fusion Drive to see if that fixes it.

1. Boot into Internet Recovery by holding Option-Command-R at startup
2. Open Terminal from the Utilities menu
3. Follow these instructions to split the Fusion Drive
4. Follow these instructions to recreate the Fusion Drive

The process looks daunting but it's straightforward if you follow the instructions precisely.

Alternatively Apple Support can guide you through the process over the phone, or the Genius Bar could do it for you.

 

[nitropowered]

Its donezo. I was on the phone for 45 minutes with Apple Support. Internet Recovery boots up then just restarts. I have an Genius bar appt tomorrow. Looks like something is fried in the computer. Hopefully they fix it for free.

 

[nitropowered]

Apple store said either the spinning drive or the SSD is dead and they won't know more until they crack it open and manually test. They had to order parts. Worst case scenario is they replace both and was quoted ~$600!

 

[Fishrrman]

OP:

Do you still have access to "a working Mac"?

What I would suggest:
FORGET ABOUT High Sierra.
See if you can download a copy of Low Sierra (10.12), and then create a bootable flashdrive using that OS installer instead.
Then, see if you can boot the problem iMac.
If you can, are you able to erase the fusion setup using Disk Utility?

I would see if I could get either one or both of the internal drives re-initialized to Mac OS extended with journaling enabled.
I've never encountered a fusion drive, so I can't tell you how current versions of Disk Utility react when you try to Erase/re-initialize a problem fusion drive setup.

If you can re-create the fusion drive, do that.
If you CAN'T do that, see if you can get both drives initialized as "standalone" -- i.e., separate SSD and HDD.
If you CAN get that done, do an OS install on the SSD portion.

I think "the key" to your "going further" at this point is to go back to Low Sierra and try from there...