Sometimes your Windows PC may fail to boot. While the main cause could be any number of things this post will focus on a corrupt/missing EFI partition.
*DISCLAIMER* The information in this post is provided without any guarantees and may cause data loss ensure you have good backups before proceeding, you have been warned!
First boot from your windows installation disk and go to the command prompt (Pressing Shift+F10) in some cases a simple
bootrec /rebuildBCD
can be executed and the computer will boot fine however in some cases you might need to rebuild the EFI partiton from scratch to do this you will need to assign the EFI partition a drive letter with diskpart
diskpart
List and select the computer’s disk (This is normally disk 0 but check)
list disk
sel disk 0
List the volumes and select the EFI volume, this is normally between 100Mb and 300Mb and is formatted with FAT32
list vol
sel vol 2
assign letter=v:
exit
Now we need to run two commands to rebuild the boot structure and the BCD store
bootrec /rebuildBCD
bcdboot D:\windows /l en-us /s V: /f UEFI
Both these command should complete successfully and your system should now be bootable once again
