I done messed up trying to change MBR to GPT, and can't access the version of windows installed on this drive

laowai · October 23, 2021

When I built my computer, apparently I formatted my SSDs to MBR. Well, I wanted to upgrade to Win11, and of course it wouldn't let me because I wasn't using UEFI with secure boot activated. So, I saw that I could convert my MBR to GPT without data loss, so I did... Well, the data is all still there. However, I can not boot from this disk. I had 2 SSDs (NvMe) installed and I had a version of windows installed on each. After I converted the 1 drive I still couldn't find it when I changed the BIOS to UEFI, so I kept messing around, and then I couldn't get the computer to boot at all. It was stuck in a loop. I bought a 3rd SSD (I know, I wanted more space anyway) I installed windows 10 in GPT from the start, and I have the cpu up and running again.

The thing is, is the 2TB drive I originally swapped from MBR to GPT has a lot of settings and programs and such, that it's the version of windows I'd prefer to upgrade. And everything is still on the drive, I just can't boot from it. I can't use the USB method of entering windows installer and repairing the drive or anything else. I tried reinstalling the boot partition, but when I compare the drive to the current bootable drive, the partition information looks different. Like I am still missing something related to booting windows. E: on Disk 1 in the photo is the partition with the version of windows I want access to. It seems like there must be a simple solution, since all the data remains, it seems like I'm just missing one thing.

Any help would be greatly appreciated.

PwnyTheTiger · October 23, 2021

You could boot off a Windows recovery USB and dive into using diskpart, I believe the command retain would be the one to look into inside diskpart but I could be grossly wrong. How exactly did you convert the disk from MBR to GPT? Did you use a 3rd party tool? mbr2gpt? diskpart?

laowai · October 24, 2021

I used EaseUS disk partition manager I believe. I tried that route with the command prompt, but so far it didn't work. Not sure what I'm doing wrong.

PwnyTheTiger · October 24, 2021

You could try using the mbr2gpt tool built into Windows and see if it manages to fix whatever the problem is, as it is now, I'm sort of stumped because I see the EFI partition on the disk in question. https://docs.microsoft.com/en-us/windows/deployment/mbr-to-gpt

If that doesn't work I found this solution using diskpart, it would appear the system boot record was probably borked using whatever software you did.

https://www.quora.com/How-boot-windows-10-after-I-had-converting-my-disk-from-MBR-to-GPT