How do I make a bricked Windows disk bootable after MBR to GPT conversion on Mac Pro 5,1?

Mac Pro 5,1

Two Mac OS partitions Running Siera and High Siera respectively.

Windows on seperate SSD drive.

Cloned Win SSD before MBR to GPT and managed to get the clone to boot and run, but need to know if I can fix the SSD Win disk before I do anything else.

Win SSD reads fine in USB enclosure on another machine, all data present and correct.


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Earlier Mac models

Posted on May 22, 2025 07:12 PM

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May 25, 2025 02:39 PM in response to NikRhodes

You cannot easily since MBR booting is different than booting as UEFI for a GPT partition. It may not even be possible on a Mac since it is a Bootcamp installation which is not quite the same as a pure Windows installation on a standard non-Apple PC.


You can try booting the Windows installer to see if you can access the Startup Repair option. Here is an example of what I mean, but you will need to boot from the Windows installer to access it since you cannot boot Windows to access "recovery mode" for Windows :

https://support.microsoft.com/en-us/windows/startup-repair-85deb0b9-fa3d-44a3-a3d0-d0f1515c2c9b


Or maybe just reinstall Windows over top of itself.

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How do I make a bricked Windows disk bootable after MBR to GPT conversion on Mac Pro 5,1?

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