Unable to install Windows 10

The 2014 Models are the last models which support both EFI and BIOS installation of Windows.

• If you use EFI, the disk partition should be GPT-only.
• If you use BIOS, the disk is a GPT disk, with a Hybrid MBR overlay.

EFI is a relatively 'faster' boot.

Multiple W10 ISO causing BSODs, points to other causes.

• What brand/model is your USB2 Flash drive?
• What is the GPU on your iMac?
• If Windows was previously installed, do you know if it was installed on a pre-Mojave macOS version? Mojave has EFI updates bundled as part of the macOS update.

The steps should be

• Boot into Internet Recovery and rebuild the APFS Fusion to CoreStorage Fusion. You should backup any important files before you do this.
• Install Sierra
• Run BC Assistant and partition and install Windows. Ensure that you use EFI Boot.
• Once you have verified both OSes, upgrade Sierra to Mojave
• Verify both OSes again

Download and install GPT FDisk from https://sourceforge.net/projects/gptfdisk/ .

Rebuild MBR to match the new GPT information thus resetting the Hybrid MBR. Use defaults for other questions (like partition codes). The only values that need modifications are the Boot flags and step 10. Accept all other defaults that Gdisk offers. Please see thesample Q&A as an example. These steps can be repeated if you make a mistake before you get to Step 12, otherwise start from Step 1 for these steps. Step 6 has numbers which are typed with a space between the numbers. Please see the sample Q&A before you execute these steps.

1. Sudo gdisk /dev/rdisk0
2. P (Print list of parts)
3. R (Recover)
4. O (print current Hybrid MBR)
5. H (chooses Hybrid)
6. Partitions numbers to be hybridized: 2 3
7. Y (Good for GRUB question)
8. N (part 2 boot flag)
9. Y (part 3 boot flag make NTFS bootable partition)
10. O (print current Hybrid MBR)
11. W (Write the new MBR)
12. Y (Yes! write the new MBR)
13. Reboot

Here is sample Q&A for this section. Please notice the Press Enter/Return.

Place EFI GPT (0xEE) partition first in MBR (good for GRUB)? (Y/N): Y

Creating entry for GPT partition #2 (MBR partition #2)

Enter an MBR hex code (default AF): Press Enter/Return

Set the bootable flag? (Y/N): N

Creating entry for GPT partition #3 (MBR partition #3)

Enter an MBR hex code (default 07): Press Enter/Return

Set the bootable flag? (Y/N): Y

Test 1 - Does Bootcamp Volume show up in Finder?

Test 2 - Can you see files in Bootcamp Volume?

Test 3 - Can you select Bootcamp in System Preferences -> Startup Disk?

Test 4 - If Test 3 is successful, select Bootcamp and Click Restart.

Ananbe wrote:

What's the best way to remove the GPT and rebuild it?

Let us do the Internet Recovery method. In IR, click on Utilities -> Terminal.

• Destroy the current GPT
  • diskutil unmountDisk disk0
  • sudo gpt destroy /dev/disk0
• Create an empty GPT
  • sudo gpt create -f /dev/disk0
• Add GPT entries in sequence, and unmount as necessary.
• EFI
  • diskutil unmountDisk disk0
  • sudo gpt add -i 1 -b 40 -s 409600 -t efi /dev/disk0
• macOS
  • diskutil unmountDisk disk0
  • sudo gpt add -i 2 -b 409640 -s 1370079192 -t apfs /dev/disk0
• Bootcamp
  • diskutil unmountDisk disk0
  • sudo gpt add -i 3 -b 1370488832 -s 583034880 -t windows /dev/disk0
• Post the output of
  • sudo gpt -vv -r show /dev/disk0
  • diskutil list

For rebuilding the MBR, would I just be doing what you wrote before with GPT Fdisk?

Yes, but not say 'y' to the additional space question. GPT to MBR is a 1:1 mapping.

Mojave defaults to EFI. The BSoD will also occur with BIOS, so switching Modes is not a prudent step.

If W10 1803 installs correctly, does it also complete the installation of BC drivers, before it crashes?

The AMD GPU is the most likely one causing issues. I have stayed with Sierra on this specific iMac model, partly due to APFS Fusion.

Do you want to consider falling back to Sierra, because High Sierra and Mojave both have APFS.

Ananbe wrote:

I'm just curious. Is this really a good idea? It seems like it'll be a downgrade to go from GPT to MBR. I don't know why I couldn't install windows before with EFI and GPT. Do you have an idea why?

Your installation came from Yosemite, which should have been BIOS/MBR. Mojave upgrade removed the MBR, that Yosemite had in place. If you can see Windows files, the NTFS part is intact, but boot-ability is missing, due to the missing MBR.

If you want to install using EFI, the current installation cannot be converted. It must be removed and you should choose EFI, but you will back to your original issue.

2013-2014 Macs which support both EFI and BIOS seem to have issues with Mojave and the corresponding BCA.