If you have a Linux live distro, or a bootable gparted, it's the partition that Linux marks as "boot".
As far as i know i do not have a linux live distro or a bootable gparted - i have never come across either
Addendum:
What I was basically suggesting is to set your bootmgr entry in the BCD first to D (like you did), and
"the operation completed successfully"
bcdedit.exe /set {312b4eb6-34b5-11de-956e-806e6f6e6963} device partition=X:
when i replace the x: with d: i get
"the operation completed successfully"
Ok, so instead of D, for the above command, try running F. And then do the same for the below command.
bcdedit.exe /set {312b4eb6-34b5-11de-956e-806e6f6e6963} osdevice partition=X:
when i replace the x: with d: i get "
the element data type specified is not recognized or does not apply to the specified entry. Run "bcdedit /?" for command line assistance"
when i replace he x: with e: i get "
an error occurred while attempting to reference the specified entry. the system cannot find the file specified"
when i replace the x: with f: i get "
the element data type specified is not recognized or does not apply to the specified entry. Run "bcdedit /?" for command line assistance"
when i replace the x: with c: i get "
the element data type specified is not recognized or does not apply to the specified entry. Run "bcdedit /?" for command line assistance"
if i leave it at x: i get "
the element data type specified is not recognized or does not apply to the specified entry. Run "bcdedit /?" for command line assistance"
I stil get the same results: for the first command bcdedit.exe /set {312b4eb6-34b5-11de-956e-806e6f6e6963} device partition=F:
"I get The operation completed successfully"
for the second command bcdedit.exe /set {312b4eb6-34b5-11de-956e-806e6f6e6963} osdevice partition=F:
I get "
the element data type specified is not recognized or does not apply to the specified entry. Run "bcdedit /?" for command line assistance"