I can install Windows 10, but not MacOS on my iMac (Paragon disk manager). HELP!

You should never use any third party utility (or a utility from another OS even) to manage a volume since they may not adhere to the native OS standards. For example use macOS utilities to manage macOS partitions. Use Windows utilities to create and manage Windows file systems and partitions. Same goes for Linux.

While I don't use Bootcamp, I believe you should not resize the partitions or Windows will become unbootable since the Window's bootloader will no longer be able to find the Windows system files.

Boot into Recovery Mode and use Disk Utility to completely erase the whole physical drive. You may need to click on "View" within Disk Utility and select "Show All Devices" before the physical drive appears in the left pane of Disk Utility. After you have properly erased the SSD you should reinstall macOS. Then run Bootcamp Assistant to resize the partitions for Windows and to create an Apple compatible Windows installer.

If the original drive is in working order, then you can use Carbon Copy Cloner to clone the macOS partition to a freshly erased SSD. Then you can use Bootcamp Assistant to resize the partitions and install Windows.

I am so frustrated that I ordered a new motherboard yesterday, …

That was a complete waste of money and will change nothing. Send it back when it arrives.

Note: You will lose everything on the drive with the following steps.

Restart the Mac and hold down the Command+Option+R keys to boot into Internet Recovery mode. Once at the work screen, launch Disk Utility from the top menu bar.

At the very top left of Disk Utility, click the arrow next to View and change it to Show All Devices.

Highlight the drive name at the very top in the left column, such as shown here. Not a container or partition name.

Click the Erase button in the top center row. Give it any name you want. Make sure APFS and GUID Partition Map are selected. Click Erase. This should only take about 20 seconds. Quit Disk Utility when it's done erasing the drive.

That will take you back to the work screen. Choose to install macOS. By default, a Command+Option+R startup will install the latest OS your Mac supports. If you use Command+Option+Shift+R, it will install the OS your Mac shipped with, or the closest to it if that version isn't available.

@Kurt Lang has advised you well on what to do.

The reason macOS may be running slow is that macOS 10.8 wasn't aware of SSDs. If Mountain Lion didn't partition the SSD on a 4K boundary then the SSD will be very slow. Actually Apple and other operating systems typically partition an SSD on a 1M boundary.

Make sure to boot into Internet Recovery Mode using Command + Option + R to hopefully boot into the latest supported version of macOS so that Disk Utility can properly format the physical SSD as described by @Kurt Lang.

If the user has 32bit apps, then Catalina should not be installed without asking permission. If Internet Recovery Mode doesn't work or you want to install another older version of macOS, then use your Mac to create a bootable macOS USB installer. macOS 10.13+ includes a system firmware update within the installer which may also help with any remaining SSD issues.

A Logic Board will not help you here. At most all you would need to do is to clear the Logic Board's NVRAM with a PRAM reset to reset the system's default boot settings. Erasing the physical drive will take care of any remaining bootloader issues.

Macs can be very particular about the USB sticks used for booting. I've found that many USB sticks are of very poor quality (sometimes even name brand ones). If you have a spare external drive you could use it as the installer drive (it may actually be faster & more reliable than a USB stick).

What is the make and model of the SSD you installed? Is the SSD a standard SATA SSD or is it a PCIe SSD? Not all SSDs are compatible with Macs.

macOS can be very particular with the installed hardware. I've encountered a few newer Macs where macOS will not run at all due to a hardware issue, whereas I can install and run Linux perfectly fine on the same system.

To see if the system firmware has been updated by the macOS installer create a bootable Knoppix Linux USB drive using Etcher (Mac/Windows/Linux). Get Knoppix v8.2 instead of v8.6 since I've had issues with the new release. Option Boot the Knoppix USB drive and select the orange icon labeled "EFI". While Knoppix boots the system may appear to be frozen on the Apple boot picker menu so give Knoppix lots of time to finish booting.

Once Knoppix boots open a terminal app (icon should be on the lower left of the Taskbar). I'm not sure which specific command will give you the system BootROM version, but one of these two should include it although it may not be listed as "BootROM". The system firmware should appear either in the format of "iMacX,Y.xxxxxx" for the old style or something like an IP address "186.0.0.0.0" for the new style.

sudo  dmidecode  -t  bios
sudo  dmidecode  -t  system

Is the original hard drive in working condition? If so does it still work in this computer? If so, then I would recommend cloning the original drive using Carbon Copy Cloner and see if the new SSD will boot Ok as this will eliminate any macOS installer issues.

If the original drive no longer works, then you may have other issues. You may want to run a memory check using Memtest86. You can use Etcher to create a bootable Memtest86 USB drive. Can you boot the Apple Diagnostics on this computer (I'm not sure if this one allows booting to the online diagnostic, but it is worth a shot).

If the SSD is a 2.5-in SATA SSD, it is installed in the SATA slot, that is typically reserved for Fusion configurations. A missing blade 'primary' SSD will cause issues. If the SSD came from a 2011 MBP, it is very unpredictable. Did you client bring you the 2011 MBP SSD. I am not aware of any 2011 models using a SATA SSD. They typically use a 2.5-in SATA HDD (5400rpm/7200rpm).

I do not recommend using it on the 2012 iMac. I suggest finding a blade SSD and putting it in the designated slot to install macOS.

Which model do you have?

iMac (27-inch, Late 2012) - Technical Specifications

iMac (21.5-inch, Late 2012) - Technical Specifications

Notice the Storage options in each.

Paragon software does not update Firmware, BootROM, SATA controller firmware, etc.,. However, it may have triggered a faulty update.

Was the SSD disk erased (on the 2012 Mac) before it was installed in the 2012 Mac? If it was not, you ran the 2011 MBP EFI on a 2012 Mac, which will cause quite a bit of grief. Take a look at About EFI and SMC firmware updates for Intel-based Mac computers - Apple Support and verify that you are running the appropriate version.

Assuming you erased the whole physical drive and not just a drive volume such as "Macintosh HD", then you appear to have some other hardware issue, but it could be anything (power supply, MLB, SATA Cable, drive, maybe even memory, or an external device). Just because a part is new doesn't necessarily mean it is good or even compatible with the Mac.

If you are currently testing with an SSD, then run the following command from the Terminal so I can see the partitioning layout of the SSD:

diskutil  list

Even if the partitions are properly aligned, early versions of macOS may still have problems with an SSD.

If you installed a memory upgrade, then remove it and reinstall the original Apple memory in the original slots. Installing memory into the wrong slots could affect performance. IIRC two memory modules should both show up as DIMM0 in the System Profiler.

BTW, is this a 21.5" or a 27" model? Do you have to remove the Logic Board to access the drive or memory?

Firmware can be re-flashed at Apple Store, but given the current conditions, getting to an Apple Store is a challenge in itself.

Do you have access to a second Mac? If yes, we can try Target Disk Mode, which allows the internal blade SSD (or any internal disk on the iMac) to be used for booting another Mac, and check the behavior and performance. If there is a Firmware issue, the second Mac should show much better behavior.

Areyou486 wrote:

Anyway, I'm going to try more suggestions here, but found something curious and interesting. When I tried to run diagnostics using the "D" key on startup, I get an error!

error 0x8000000000000003, cannot load 'EFI/Drivers/TestSupport.efi'

Unfortunately this is a common issue with the Apple Diagnostics with some of the newer system firmware on some Logic Boards. Apple broke it and never fixed it for some systems.

Since it tries to boot macOS my guess would be a memory or GPU failure since it happens with two different Logic Boards. Try running Memtest86 to check the memory.

Areyou486 wrote:

I used disk Utility "restore" function...

A TM backup/restore is much cleaner, provided the new SSD was reformatted in the 2012 Mac.

Right now I have the screen off and put a brand new SSD in it and am attempting to load Mountain lion from the internet recovery option... Nothing but monitor and keyboard/mouse attached.

If you have another Mac, do you want to consider Target Disk Mode to diagnose issues with this iMac further? See Use target disk mode to move files to another computer - Apple Support for reference.

Hello Areyou486,

Thanks for that info and for choosing the Apple Support Communities. If I understand correctly, you are unable to reinstall macOS on an iMac after installing Paragon Hard Disk Manager for Mac, but you're able to install Windows 10. To help with this, please see these resources from Paragon, including contacting them for help with their software:

Hard Disk Manager For Mac – Troubleshooting Guide > Knowledge Base

Paragon Software Group - Technical Support

Cheers!

Since that Apple article is no longer up to date (I believe the firmware listed in @Loner T's link is most likely from macOS 10.12 Sierra), a better reference to current firmware revisions by macOS can be found in these posts. I've listed the OS versions which is just a rough guide since there is some overlap due to security updates and such.

For the most part if a system has a BootROM version that looks like an IP address, then it is the newer style (although there are some exceptions) which includes support for Internet Recovery Mode on older systems and includes NVMe support for systems with PCIe SSDs.

macOS 10.13 High Sierra firmware revisions:

https://eclecticlight.co/2018/06/27/which-efi-firmware-should-your-mac-be-using-version-2/

macOS 10.14 High Sierra firmware revisions:

https://eclecticlight.co/2018/10/31/which-efi-firmware-should-your-mac-be-using-version-3/

macOS 10.15 Catalina firmware revisions:

https://eclecticlight.co/2019/10/08/which-efi-firmware-should-your-mac-be-using-version-4/

This site includes a lot of good articles and information, although I do disagree with some of his articles. Overall though there is a lot of useful information.

I still suspect there is an issue with the EFI, …

If there is, it would be an issue with the drive itself. That's where the EFI boot partition is.

Are these El Capitan / High Sierra / Catalina installers local? That is, they're on a flash drive you're installing from, and they still don't finish even overnight?

Areyou486 wrote:

I restored the OS to the SSD from the 1T drive originally, then reformatted a few times in my various attempts...

Can you describe the exact steps? Restoring the OS does not delete the EFI partition, if you use Time Machine, for example.