Recently, One of our customer’s server had an issue during boot process. Below the steps on how to resolve UEFI Boot issue on Windows Server.

You need to insert and boot into Windows Server Disk / ISO and open the command prompt through “Repair Windows” selection.

Please be aware to take necessary precaution before attempting this.

Once you have your command prompt, use the DISKPART tool to verify that the UEFI partition has a drive letter assignment.

Enter DISKPART

DISKPART> select disk 0

Disk 0 is now the selected disk.

DISKPART> list vol

There was no drive letter assignment to our UEFI partition (volume 3) so we need to assign a drive letter.

DISKPART> sel vol 3

Volume 3 is the selected volume.

DISKPART> assign letter=E:

DiskPart successfully assigned the drive letter or mount point.

Exit DiskPart tool

Next, we need to change to the boot folder on the UEFI volume.

Change to the UEFI volume into the boot folder. Depending on the way Windows was installed this path maybe one of the following.

cd /d E:\Boot\

cd /d E:\EFI\Microsoft\Boot\

cd /d E:\ESD\Windows\EFI\Microsoft\Boot\

Now we will need to enter three command lines to repair the BCD store. Again depending on the way Windows was installed these may not all be necessary, however
command lines are are unnecessary will not affect the outcome.

  1. bootrec /fixboot
  2. bootrec /fixmbr
  3. bootrec /rebuildbcd

source: https://ecognosci.wordpress.com/2016/03/28/repair-corrupt-bcd-uefi-windows-server/