Resolving converting MBR to GBT converting boot issue

Megahertz said:

To do a offline conversion, you should boot from a Win 10 Installation drive, launch a CMD window (Shift+F10) and run mbr2gpt.

I already tried that, why I posted the question.

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Hopefully this is clearer.

Megahertz said:

You have two drives (E: and C:) with an Active partition, one reason mbr2gpt can't know witch one to convert.
- Set E: an non active (can be made with disk manager or diskpart)

Code:

diskpart
select volume E
inactive
exit

- Detach (SATA or power cable) of ALL other drives from MB. Leave only C: attached.
- Disable Win RE. Run reagentc /disable.
- Boot from Win 10 or Win 11 installation drive and launch the CMD window. Run mbr2gpt /validate. If everything is ok run mbr2gpt /convert.
- Change BIOS mode to UEFI.
- Boot the drive as UEFI.
- Run Reagentc /enable
- Shut down and attach all other drives to the MB

I assume setting it as non-active won't cause data loss, in any case I'll have a back up ?

JerometheGiraff said:

I already tried that, why I posted the question.

if this was the message it isnt very enlightening

MBR2GPT: Attempting to convert disk 3MBR2GPT: Retrieving layout of diskMBR2GPT:
Validating layout, disk sector size is: 512 bytesMBR2GPT:
Trying to shrink the OS partitionMBR2GPT:
Creating the EFI system partitionCannot create EFI system partition.
Error: 0x000036B7
MBR2GPT-undo:
Extending back the OS partition
MBR2GPT: Conversion failed

You might have better luck if you delete the non live recovery partition, or run reagentc /disable, then delete both of them .

Since C: is marked as both the system and boot partition, the computer is booting from it, which is the drive that mbr2gpt will recognize as the system drive and try to convert. I would run, in command prompt with admin:

Code:

reagentc /disable

Then delete the two recovery partitions that are after C: drive.
Then attempt mbr2gpt again.

What do you mean delete the two recovery partitions that are after C:; I don't want to delete a partition that has data on it.
All I should do for E, which is the the drive causing the issue is make it inactive then run mbr2gpt on C ?

JerometheGiraff said:

What do you mean delete the two recovery partitions that are after C:; I don't want to delete a partition that has data on it.
All I should do for E, which is the the drive causing the issue is make it inactive then run mbr2gpt on C ?

Changing E: drive will have no effect on running mbr2gpt on C: drive. I gave you the solution, in my experience, that had the greatest chance of success.

NavyLCDR said:

Changing E: drive will have no effect on running mbr2gpt on C: drive. I gave you the solution, in my experience, that had the greatest chance of success.

I hope no data is lost after running this; reagentc /disable on the C drive from a rescue disk.