*Here to assume that disk 0 is a booting device.

a) After you boot your computer using Windows 8 DVD or System Repair Disc, a black screen
appears with gray text “Press any key to boot from CD or DVD“. Press any key.
b) Select the correct time and Keyboard type.
c) Click Repair your computer in the lower left corner.
d) Select Troubleshoot from Choose an optionscreen.
e) Click Advanced options in Troubleshootscreen.
f) Click on Command Prompt.
g) Type these following commands and hit enter after each line of command:
“#” is an instruction comment so not to type it 😉

# to execute diskpart program
DISKPART> list disk
DISKPART> select disk 0
DISKPART> list volume
# find your system partition with fat32 file system. Here to assume it as volume 2.
DISKPART> select volume 2
# To assign drive letter.
# If you want to remove drive letter, use remove command.
DISKPART> assign letter=b:
# To terminate diskpart command.

# Now, you sould move to b:\EFI\Microsoft\Boot\, as windows stores BCD in this folder.
cd /d b:\EFI\Microsoft\Boot\
# this is not necessary.
ren BCD BCD.bak
# To write a new bootsector on your system partition.
bootrec /fixboot
# If your windows running, you should do from here.
# To create BCD store. “/f ALL” is to update BIOS setting including UEFI firmware/NVRAM.
# Replace “ja-JP” with your language or remove “/l” option if you use English, of course.
# It might be sense only typing “bcdboot c:\Windows“.
bcdboot c:\Windows /l ja-JP /s b: /f ALL

That’s that. Booting information of your PC has been written over.

Let’s reboot and see whether it go fine or not!”
A couple things to note. First, when using command select disk, this is referring to your Windows 10 boot/repair media located in your CD or USB drive. Second, at the final step I was a little confused by the wording when addressing the language. The command I used was bcdboot c:\Windows /l en-US /s b: /f All. That’s about it! I was just about ready to wipe everything out and do a fresh install, so I’m incredibly glad I found this post.