When Windows 10 Won’t Boot (for UEFI Systems)

FOR~GO
(For Geeks Only)
By Joe Callison
7 February 2019

There are many possibilities for why Windows 10 fails to boot, so troubleshooting involves a process of elimination. Start with the simplest and least risky possible fixes. If the recovery partition exists, failing to start the third try should automatically bring up the Windows Recovery Environment (WinRE). If not, there are other methods to get it as outlined in this Microsoft link, along with several things to try once there:    
https://support.microsoft.com/en-us/help/4026030/how-to-use-windows-recovery-environment-winre-to-troubleshoot-common-s
For more detailed help in using DISM, see the following:

https://www.windowscentral.com/how-use-dism-command-line-utility-repair-windows-10-image

If none of the above works, then more complicated measures are needed. Use one of the methods to get the Command Prompt (as Administrator) through the Windows recovery environment, my preferred method is to boot from installation media and press shift+F10 at the first screen when the country and keyboard selection is displayed, and use the following commands one at a time, followed by enter after each command. WARNING- IT IS STRONGLY RECOMMENDED TO MAKE A BACKUP OF YOUR PARTITION(S) CONTAINING THE OPERATING SYSTEM AND USER DATA BEFORE PROCEEDING. If you accidentally delete your Windows or data partitions, then software to recover the deleted partitions will be needed if no backup is made:

FIX #1- Rebuild BCD data from existing Windows Installation

Diskpart
List disk
Select disk 0  (or whichever is the large one containing your Windows system if more than one is listed)
List partition  (you should see at least 3 partitions: System-or EFI, Reserved-or MSR, and Primary-or Windows, OS, etc. If you have these 3 partitions, then continue with the following commands)
List vol  (the EFI System volume should be FAT32 and a few hundred MB in size)
Select vol x  (where x is the EFI System volume number determined above)
Assign letter=s  (any unused volume letter will do, skip if it already has a letter assigned)
Exit  (closes diskpart)
Cd /d s:\efi\microsoft\boot\  (where s is the volume letter chosen above, if the system can’t find the path, try using dir and cd commands to find the correct path to the Boot directory)
Bootrec /fixboot  (bootrec.exe is a utility only available in the recovery environment)
Ren BCD BCD.bak
Bcdboot c:\Windows /1 en-us /s s: /f ALL  (the /1 en-us /s s: /f ALL is optional and only needed to boot in both UEFI and BIOS systems, c:\Windows is the path to the directory with Windows installed, this command copies the BCD data from the Windows installation)
Bootrec /scanos
Bootrec /rebuildbcd    

Restart the computer, when the Windows Boot Manager appears in the list of bootable devices, choose desired operating system to start. If it still does not boot, try running the Startup Repair again and if that fails, go to the next method below.

FIX #2- Delete and/or Recreate EFI and MSR Partitions
(also useful if you migrated only your operating system partition to a new disk)

Go to Command Prompt as Administrator again and enter the following commands:
Diskpart
List disk
Select disk 0  (or whichever contains the Windows system)
List partition
Select partition 1  (or whichever number is the EFI System partition)
Delete partition override
Select partition 2  (or whichever number is the MSR reserved partition)
Delete partition override
List partition  (make sure all partitions before the Windows partition are now gone)
Select partition 3  (or whichever number is the Windows partition)
Shrink desired=500  (shrink the Windows partition by 500 MB)
Create partition EFI size=200
Format quick fs=fat32 label=”System”
Assign letter=s  (any unused letter will do)
Create partition msr size=128
Exit  (closes diskpart)
Cd /d s:\efi\microsoft\boot\  (where s is the volume letter chosen above, if the system can’t find the path, try using dir and cd commands to find the correct path to the Boot directory)
Bootrec /fixboot
Bcdboot c:\Windows /1 en-us /s s: /f ALL  (the /1 en-us /s s: /f ALL is optional and only needed to boot in both UEFI and BIOS systems, c:\Windows is the path to the directory with Windows installed)

Reboot the computer. If it still does not boot, try running the Startup Repair again and if that fails, a more manual method of repairing EFI bootloader and Windows BCD may be needed, which may be beyond the skills of most non-experts, but is outlined in the following:
http://woshub.com/how-to-repair-deleted-efi-partition-in-windows-7/

All of these fixes are based on existence of an uncorrupted Windows partition. If it is corrupted and cannot be repaired with DISM, then a reinstallation of Windows may be your only viable solution.

Posted by Joe Callison

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