Fix Boot Manager Failed to Find OS Loader in Windows

This error appears when Windows Boot Manager cannot locate the OS loader. The system partition, BCD store, or boot mode may be wrong.

Background and causes

It can happen after cloning, deleting a system reserved partition, changing active partitions, or switching between Legacy and UEFI boot.

• Confirm the exact disk, partition, drive letter, file system, and capacity before changing anything.
• Recover or back up important files before formatting, deleting, converting, or recreating partitions.
• For boot-related changes, check BIOS/UEFI mode and boot order before editing disk layout.

Use Windows built-in tools

Boot from Windows media, run Startup Repair, assign a letter to the EFI or System Reserved partition, and rebuild boot files with BCDBoot after confirming the Windows drive letter.

Use Qiling tools for guided steps

Qiling Disk Master

Repair boot records or rebuild MBR from a bootable environment with a clear operation preview.

• Free Download
• Windows 11/10/8.1/8/7,100% Secure

Function 1. Fix Windows boot files

Use this function when the system disk is detected but Windows cannot load because boot files, BCD information, or startup drivers are damaged.

Step 1. Start the computer from Qiling bootable media, open Qiling Disk Master, and confirm that the Windows system disk is detected.

Step 2. Open Tools and utilities, select Fix Boot, and enter the boot repair window.

Step 3. Select the Windows system partition or boot partition that belongs to the failed installation. If needed, check Fix main drivers, then click Proceed.

Function 2. Rebuild MBR for Legacy BIOS boot

Use this function only when the computer boots in Legacy BIOS mode and the Windows disk uses MBR. It is a separate repair from Fix Boot, so do not use it for a UEFI/GPT boot disk.

Step 1. In Qiling Disk Master, select the system disk that contains the Windows installation.

Step 2. Right-click the disk and choose Advanced > Rebuild MBR.

Step 3. Select the MBR type that matches your Windows version, then click Proceed to execute the operation.

Check the result

Remove the repair USB, restart, and verify that Windows Boot Manager is first in BIOS or UEFI.

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