Repair Windows Boot Files and BCD: UEFI BCDBoot or BIOS bootrec

Windows cannot boot, and Startup Repair has not resolved a boot-data error. The repair depends on the firmware mode and system partition, not just the letter assigned to your Windows folder. Modern UEFI/GPT installations normally store BCD on the EFI System Partition at \EFI\Microsoft\Boot\BCD; BIOS/MBR systems normally use \Boot\BCD on their system partition.

Back up accessible files before manual boot repair, keep the BitLocker recovery key outside the PC, and stop if the disk reports read errors or partitions are missing. Do not format, clean, delete or mark an arbitrary partition active to make a repair command succeed. Boot changes can affect dual-boot/custom configurations.

Step 1: Use Windows Recovery and Startup Repair

Boot official Windows installation/recovery media in the mode appropriate to the installed system. Choose Repair your computer → Troubleshoot → Advanced options → Startup Repair. If it fails, open Command Prompt from those recovery options and inspect the layout before writing boot files.

Step 2: Identify the installed Windows and system partitions

Recovery drive letters can differ from those used in normal Windows. These commands only list the disks and volumes:

diskpart
list disk
list volume
exit

Check the actual Windows folder with dir on the relevant volume, for example:

dir D:\Windows

Use D: only if that is the verified installed Windows volume. An encrypted/locked volume must be unlocked through the supported recovery process before its contents can be inspected.

On a UEFI/GPT system, identify the EFI System Partition belonging to that Windows disk. It is normally FAT32, but size or file system alone is not enough to select it; multiple disks can have multiple EFI partitions. If unsure, have an administrator identify it. In DiskPart, select that verified volume and assign an unused temporary letter (for example S:). Do not format it.

Step 3: Recreate UEFI boot files with BCDBoot

Before changing an existing store, copy its BCD and any custom boot configuration to verified external storage. Microsoft’s BCDBoot copies boot files from the installed Windows folder to the selected system partition.

Example only: if installed Windows is verified as D:\Windows and its verified EFI System Partition has been assigned S:, the UEFI command is:

bcdboot D:\Windows /s S: /f UEFI

Check the success/error result before restarting. The explicit /s option chooses the system partition; on UEFI it does not create a Windows Boot Manager NVRAM entry. Verify the firmware’s existing Windows Boot Manager entry or follow the manufacturer/Microsoft procedure if a firmware entry also needs repair. Do not assume copying files alone fixes every firmware-entry problem.

Step 4: Keep BIOS/MBR repair separate

For a verified BIOS/MBR installation, Microsoft’s startup troubleshooting includes bootrec /fixmbr, bootrec /fixboot, bootrec /scanos and bootrec /rebuildbcd as applicable. Those are not a universal UEFI repair sequence. An MBR rewrite can replace a custom bootloader.

BCDBoot can also populate the verified BIOS system partition with /f BIOS; the system partition may be separate from the Windows volume. Follow its documented BIOS procedure for your layout rather than substituting a Windows drive letter into C:\Boot\BCD and assuming that is the active store.

FAQ

Does boot repair guarantee my files are safe? It targets boot configuration, but a wrong partition selection, an underlying failing drive or an interrupted operation can still cause problems. Back up accessible data first.

Why does bootrec /fixboot say Access is denied? Do not treat that as permission to rename C:\Boot\BCD. On UEFI, inspect the actual EFI System Partition and use the appropriate BCDBoot procedure, or return to Startup Repair.

The error returns. Check storage health and the recovery logs before repeating writes. Preserve data before intensive disk repair if the drive may be failing.

Sources: Microsoft Learn — BCDBoot firmware modes, system partition and NVRAM behavior, Microsoft Learn — Windows startup troubleshooting