You can copy the boot files to the C drive and make the partition bootable/active.
Then, restart the PC (boot from Disk 1) and run MBR2GPT on Disk 1.
From admin Command Prompt, run:
bcdboot C:\Windows /s C: /f BIOS
Post the output.
Unable to run mbr2gpt due to 'Cannot find OS partion on disk 0'
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Wehmer
20
Reputation points
Hi guys,
I am currently many steps down attempts to get my computer ready to be switched over to Windows 11. It seems to have all the missing parts in place, excluding my disc drives being MBR rather than GPT.
I am currently getting this error - Cannot find OS partion on disk 0 - when I go to validate the program to run.
I didn't set up the drives or the partitions in my system, so I'm a little unsure why they are the way they are, but was hoping I could get some help.
As you can see, Disc 0 has a System Reserved with a 'System' tag, while Disc 1 has my C: with Boot. I'm wary about changing 'primary' drives as I'm not too familiar with how partitioning works and don't want to make a step that I'm unsure about.
Any help would be advised - I've had conflicting reports about the System Reserved chunk in Disc 0 - I think because it's flagged with a System tag I need to leave it alone? I'm unsure how that works.
Any advice would be amazing.
Windows for home | Windows 10 | Settings
Accepted answer
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Ramesh Srinivasan 164.5K Reputation points Volunteer Moderator2025-08-08T02:40:35.72+00:00
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Ramesh Srinivasan 164.5K Reputation points Volunteer Moderator
2025-08-08T02:46:39.2866667+00:00 Additionally, please run the PC Health Check app to see if the system is compatible with Windows 11:
https://aka.ms/GetPCHealthCheckApp
Run the PC Health Check app, and click "Check now."
Click "See all results."
Post a screenshot.
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Wehmer 20 Reputation points
2025-08-08T11:17:03.6166667+00:00 This hasn't seemed to change anything from the partitions, though.
I'm under the impression (perhaps wrongly) that the System tag on Disk 0 is the bootloader, and making Disk 1 active will mean I am unable to boot into the computer. Are you able to confirm?
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Wehmer 20 Reputation points
2025-08-08T12:50:18.58+00:00 This did the trick - I was able to activate Secure Boot. Thank you so much - the partitions look as they should.
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Ramesh Srinivasan 164.5K Reputation points Volunteer Moderator
2025-08-08T12:50:54.1666667+00:00 You're welcome!
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2 additional answers
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DaveM121 758K Reputation points Independent Advisor2025-08-07T14:43:56.76+00:00 It seems on your system Windows was previously installed on disk 0 and was then re-installed on Disk 1 and that is causing the problem.
In the mbr2gpt command, are you typing 0 for the disk number or 1 where Windows is installed onto?
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Wehmer 20 Reputation points
2025-08-07T14:48:07.95+00:00 When I run it as normal with no disk, it automatically returns 'cannot find OS on Disk 0'.
When I use mbr2gpt /validate /disk:1 it throws up a different error: Disk layout validation failed for disk 1.
When I look into the setupact folder to see what went wrong, I get the following: ValidateLayout: Wrong boot partition count, expected 1 but found 0.
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DaveM121 758K Reputation points Independent Advisor
2025-08-07T14:51:32.9666667+00:00 Thank you for that information, in that case, you will need to backup your files from the C drive, create a bootable Windows USB and use that to clean install Windows and at the start of the instalaltion, wipe the drive and convert it to GPT.
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Wehmer 20 Reputation points
2025-08-07T15:06:16.9966667+00:00 I was hoping to avoid reinstalling the OS if at all possible - I was hoping there'd be an option to move the bootloader that is on Disk 0 and recreate it on Disk 1 in a new partition potentially, making that the active disk and having the OS and bootloader on the same Disk.
Is that doable, or is a clean install my only option?
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DaveM121 758K Reputation points Independent Advisor
2025-08-07T15:08:05.62+00:00 With your drive configuration, a clean install will be the only option.
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Wehmer 20 Reputation points
2025-08-07T22:31:30.47+00:00 Not the answer I was hoping for, but appreciate your time. Wish me luck!
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Ramesh Srinivasan 164.5K Reputation points Volunteer Moderator
2025-08-08T11:20:37.62+00:00 The command ran correctly, which means the boot files and the BCD are created on the C drive.
Now, right-click on volume C: in Disk Management and click Mark Partition as Active.
Power off the system. Power it on and boot from Disk 1 by changing the boot order in the BIOS.
Run MBR2GPT validate on Disk 1.
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Wehmer 20 Reputation points
2025-08-08T12:16:42.26+00:00 Very happy right now - will attempt to convert to GPT and report back
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