If Windows 11 fails to start and prompts "Bootmgr is missing" or "EFI boot partition not found", the problem may be that the EFI boot program is corrupted, which can be fixed by following the following steps: 1. Use Windows 11 to install the USB flash drive to enter the recovery environment; 2. Open the command prompt and run the bootrec /fixmbr, bootrec /fixboot, bootrec /rebuildbcd commands in turn to rebuild the BCD; 3. If the EFI partition is corrupt, use diskpart to allocate the drive letters and check whether the EFI\Microsoft\Boot folder exists; 4. You can try using the automatic repair tool Startup Repair. The entire process requires attention to correctly selecting disks and partitions to avoid further problems caused by misoperation.

If your Windows 11 PC won't boot and you're seeing errors like “Bootmgr is missing” or “EFI boot partition not found,” the issue might be a corrupted EFI bootloader. Fixing it isn't too complicated if you have access to a working recovery environment.

What You'll Need Before Starting

Before jumping into repairs, make sure you have:

• A Windows 11 installation USB or recovery drive (optional but helpful)
• Access to the command prompt via Safe Mode or recovery environment
• Basic knowledge of disk partitions (don't worry, we'll guide you through what's needed)

Also, this method assumes your system uses UEFI firmware — which most modern PCs do. If you're not sure, check your motherboard or laptop specs online.

Rebuild the BCD Using Command Prompt

One of the most common fixes for a broken EFI bootloader is rebuilding the Boot Configuration Data (BCD). Here's how:

1. Boot into Recovery Environment:

   • Restart your PC and keep trying to boot (you may see a black screen or error message).
   • If that doesn't work, use a Windows 11 installation USB: plug it in, boot from it, and click "Repair your computer" at the bottom-left corner.

2. Open Command Prompt:

   • Go to Troubleshoot > Advanced Options > Command Prompt.

3. Run these commands one by one:

    bootrec /fixmbr
   bootrec /fixboot
   bootrec /rebuildbcd

   These will repair the master boot record, fix the boot sector, and rebuild the BCD store respectively.

Note: If bootrec /rebuildbcd doesn't find any Windows installations, you might need to assign drive letters manually or check for hidden system partitions.

Check and Repair the EFI System Partition

Sometimes the EFI partition itself gets damaged or misconfigured. This is where the bootloader files live, so it needs to be intact.

1. In the same Command Prompt window, run:

    diskpart
   list disk
   select disk X (replace X with your main disk number)
   list partition

   Look for a small partition labeled “System” — usually around 100MB or 500MB. That's your EFI partition.

2. Assign a drive letter to it:

    select partition Y (replace Y with the correct partition number)
   assign letter=S
   exit

Now you can access the EFI partition as drive S: (or whatever letter you choose). Navigate to it and check if the folder EFI\Microsoft\Boot exists. If not, you may need to copy those files from another Windows system or reinstall the bootloader using bootrec .

Use Automatic Repair (Optional)

If you're not comfortable with the command line, try the built-in Automatic Repair tool:

• From the recovery environment, go to Troubleshoot > Advanced Options > Startup Repair.
• It might automatically detect and fix bootloader issues.

This doesn't always work, especially if the system files are severely damaged, but it's worth a try.

That's the basic process. Most EFI bootloader problems on Windows 11 can be resolved with a few command-line tools and a bit of patience. Just remember to double-check your disk and partition selections — a typo could cause confusion or unintended results.

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