Win 10 "losing" boot partition - assigning wrong letter - can't boot

Hi all -

New to this forum - 1st post

My machine is a rather interesting triple-boot box (Win 10 Pro version 1903, Ubuntu Linux 18.04, and MacOS Catalina).
Booting via UEFI. Boot manager is Clover, with GRUB secondary for Linux. Windows and Linux boot from one NvMe drive and MacOS from another. Each boot drive has its own EFI partition. There are also four other SSD drives and one spinner drive.

All has been working fine for quite some time, through multiple OS updates and hardware tweaks and upgrades.

However, recently Win10 has failed to boot, going directly to automatic repair, which fails; diagnosis fails.

Linux and MacOS continue to boot normally.

When I go into Command Prompt through Advanced options in recovery, DISKPART shows that the letter order of the partitions has been scrambled, with the Windows boot partition no longer being assigned C:. It's been assigned D: E: F: and others.

Changing the drive letters via DISKPART does not solve the problem.
BCDEDIT | find "osdevice" finds the correct partition.

However, BOOTREC /rebuildbcd does NOT find any identified Windows installations (perhaps this is because the drives are GPT-partitioned rather than MBR??)

CHKDSK /f on the boot partition -> clean.

I restored the boot partition from a cloned copy made last week - which was working at the time - no difference, same behavior.

Any thoughts? This is driving me nuts.

Thanks in advance.
Bob

Try it like this:

1) bcdedit /export c:\bcdbackup
2) attrib c:\boot\bcd -h -r -s
3) ren c:\boot\bcd bcd.old
4) bootrec /rebuildbcd

Unfortunately, the \boot directory doesn't exist.

I have everything backed up. I figured I'd do a fresh install.

However, I can't do a fresh reinstall because the 1909 (and apparently the 1903 version also) install media can't be installed on a FAT32-formatted USB drive (I need to install it in UEFI mode). Tried making the install media the usual way and removing the bootmgr file, and also tried creating it with Rufus in UEFI mode.

Turns out, this machine will not boot a UEFI USB which is formatted NTFS, which is the only format available now, since the new install.wim file is too big for FAT32.

I'm going to be bald soon, as this has me tearing my hair out. I can't repair my original install, and I can't do a clean install.

I tried unplugging all of my other physical drives beside the boot NVMe drive. However, that drive has another NTFS partition on it - and even then, *that* partition is the one that gets the C:. I suppose the last resort is to delete it and see if I can get the original install to boot. Why would *any* other NTFS partition get the C: designation?

This is driving me batty. If someone can tell me how to get the NTFS-formatted install USB to boot on this machine, I'd be very grateful. Thanks.

Malibyte said:

This is driving me batty. If someone can tell me how to get the NTFS-formatted install USB to boot on this machine, I'd be very grateful. Thanks.

Try Rufus. It will create a UFD with two partitions, one contains the NTFS drivers needed to boot. Disable Secure Boot before using it.

Open administrative command prompt and type or copy and paste:

Code:

bcdedit /enum all
bcdedit | find "osdevice"
reagentc /info
diskpart
lis dis
lis vol
sel dis 0
det dis
lis par
sel par 1
det par
sel par 2
det par
sel par 3
det par
sel par 4
det par
sel par 5
det par
sel dis 1
det dis
lis par
sel par 1
det par
sel par 2
det par
sel par 3
det par
sel par 4
det par
sel par 5
det par
sel dis 2
det dis
lis par
sel par 1
det par
sel par 2
det par
sel par 3
det par
sel par 4
det par
sel par 5
det par
sel dis 3
det dis
lis par
sel par 1
det par
sel par 2
det par
sel par 3
det par
sel par 4
det par
sel par 5
det par
sel dis 4
det dis
lis par
sel par 1
det par
sel par 2
det par
sel par 3
det par
sel par 4
det par
sel par 5
det par

When these have completed > right click on the top bar or title bar of the administrative command prompt box > left click on edit then select all > right click on the top bar again > left click on edit then copy > paste into the thread


Save the results to a flash drive > transfer the flash drive to a working computer to upload the results into this thread.

Anibor said:

Try Rufus. It will create a UFD with two partitions, one contains the NTFS drivers needed to boot. Disable Secure Boot before using it.

Already tried Rufus. Secure Boot is always disabled. This machine is 5-6 years old; the MB has the latest available BIOS, but it doesn't boot from a UEFI USB formatted with NTFS, which is the only option given by Rufus with the new install media.

Thanks.

To make a USB Win 10 installation drive (it will only boot as UEFI):
- Format the USB drive (min 8G) as Fat32.
- Copy all files and folders to the USB drive.

If you download a Iso from M$ using Windows 10 installation media, all files will be less than 4G

Remark:
If you have sources\install.wim bigger than 4G, you have to split into smaller swm files

On a Win 10 computer, move the install.wim to a working folder.
Open a CMD window in this folder and type:
Dism /Split-Image /ImageFile:install.wim /SWMFile:install.swm /FileSize:3600

Move the created install.swm files to /sources and then copy all files and folders to the USB drive

Megahertz said:

To make a USB Win 10 installation drive (it will only boot as UEFI):
- Format the USB drive (min 8G) as Fat32.
- Copy all files and folders to the USB drive.

If you download a Iso from M$ using Windows 10 installation media, all files will be less than 4G

Remark:
If you have sources\install.wim bigger than 4G, you have to split into smaller swm files

On a Win 10 computer, move the install.wim to a working folder.
Open a CMD window in this folder and type:
Dism /Split-Image /ImageFile:install.wim /SWMFile:install.swm /FileSize:3600

Move the created install.swm files to /sources and then copy all files and folders to the USB drive

Did all of this. Formatted the USB drive as FAT32, copied all of the files from the installer .iso to a directory on my SSD, did the split as above, deleted install.wim and copied all of the files (including the two *.swm files) to the USB.

The first time, it would not boot as a UEFI drive. After going back in and renaming bootmgr to bootmgr.old in the USB root directory, everything worked and I got the fresh install done. Thanks everyone !!

Now I just have to reinstall GRUB2 so I can boot Linux again. The MacOS drive was untouched.

Now...I have a cloned copy of the old C: partition. Is there any way I can recover my product key to activate Windows, or do I have to call Microsoft to get a new one?

Also - what's the best way to prevent this problem in the future (Windows losing the boot partition) in addition to simply cloning the working drive (which I *thought* I had done last week, before this all hit the fan)? I thought I had at least one system restore point set up also, but Recovery couldn't find it either.

Thanks again!