Whether you are facing the dreaded error, a "Bootmgr is missing" prompt, or an infinite loading loop, this guide will walk you through every possible method to perform a Windows Server 2012 R2 boot repair —from built-in recovery tools to advanced command-line maneuvers.

Consider a clean installation if:

To access WinRE:

bcdedit /export C:\BCD_Backup attrib c:\boot\bcd -h -r -s ren c:\boot\bcd bcd.old bootrec /rebuildbcd Use code with caution. Copied to clipboard 4. Fixing Boot Issues Caused by Updates If the server is stuck in a boot loop after an update, use in the Command Prompt to revert pending actions:

To repair the boot files, you must boot into the Windows Recovery Environment (WinRE) using the original installation media.

This is the most common fix for "Operating System not found" or boot loop errors.

bootrec /rebuildbcd

list volume select volume X (Replace X with the volume number of the FAT32 EFI partition) assign letter=S (Assigns the temporary drive letter S) exit Use code with caution. 2. Recreate the Boot BCD Store

Select your language and keyboard layout, click Next , and then click Repair your computer in the bottom-left corner. 2. Basic Startup Repair

After this, exit the command prompt and restart the server.

Always test the repaired server in maintenance mode before returning it to production.

Is your server utilizing or UEFI (GPT) firmware?

He stripped the file's "hidden" and "read-only" attributes: attrib c:\boot\bcd -h -r -s