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If Windows will not boot, start with Startup Repair in Windows Recovery Environment (WinRE). It can attempt to fix damaged MBR boot code and other startup problems. If that fails, choose a command based on the layer involved: bootrec /fixmbr writes master boot code, bootrec /fixboot writes boot-sector code, and BCD tools address boot configuration or system-partition files. None is a universal fix for every boot failure.
Before repairing: identify what may be broken
“MBR corruption” is often used as shorthand for a Windows boot failure, but several distinct components can prevent startup. Microsoft’s Windows startup troubleshooting guide lists messages such as “Boot Configuration Data (BCD) missing or corrupted,” “Boot file or MBR corrupted,” “Operating system Missing,” “Boot sector missing or corrupted,” and “Bootmgr missing or corrupted.” The wording can help you choose the right recovery path.
- Master boot code: code in the MBR that starts the boot process.
bootrec /fixmbrtargets this code. - Partition table: information about the disk’s partitions. Rewriting master boot code does not restore a damaged partition table.
- Boot sector: a separate area of boot code, addressed by
bootrec /fixboot. - BCD and system-partition files: boot configuration data and related files needed to launch Windows. These may require BCD repair or BCDBoot.
A boot error alone does not establish that the MBR is the cause. If the disk appears physically damaged or the partition layout may be affected, avoid repeated write operations and prioritize diagnosis and data preservation.
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Startup Repair is the safer first step because it can attempt fixes for several common startup faults, including damaged MBR boot code and corrupted BCD. Microsoft’s current guidance applies to Windows 10 and Windows 11. You can enter WinRE from recovery options already available on the PC or boot from Windows installation media. With installation media, use this path:
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- Boot the computer from the Windows installation media.
- At Windows Setup, select Next, then Repair your computer.
- Choose Troubleshoot, Advanced options, and Startup Repair.
- Allow the repair attempt to finish, then restart and check whether Windows loads.
On an encrypted device, have the BitLocker recovery key ready; Microsoft says it may be required to complete Startup Repair. If the attempt fails, its diagnostic log may be available at %windir%System32LogFilesSrtSrttrail.txt. Microsoft documents the repair options and BitLocker requirement in its Startup Repair guidance.
Use Bootrec only for the matching boot component
To run Bootrec commands, open Troubleshoot > Advanced options > Command Prompt in WinRE. Select the operation that matches the suspected fault rather than running every command indiscriminately.
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Repair master boot code
For suspected damaged MBR boot code, run:
bootrec /fixmbrMicrosoft states that this overwrites only the master boot code. It does not repair a damaged partition table, so it may not help if partition information or the disk itself is the problem.
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Repair boot-sector code
If the reported problem concerns a missing or corrupted boot sector, run:
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bootrec /fixbootThis targets boot-sector code, not the MBR’s master boot code. It is not a remedy for a failing drive or partition-table damage.
Repair a BCD-related startup problem
For a BCD error, Microsoft’s troubleshooting sequence begins by searching for Windows installations that are not in the BCD store:
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bootrec /scanosIf the issue remains, Microsoft documents backing up and renaming the existing BCD before rebuilding it:
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bcdedit /export c:bcdbackup
attrib c:bootbcd -r -s -h
ren c:bootbcd bcd.old
bootrec /rebuildbcdRestart after the repair attempt. These path-specific commands must target the correct offline boot files. Drive letters in WinRE can differ from their usual letters in Windows, so do not assume that C: contains the Windows installation or BCD. Microsoft’s startup troubleshooting instructions cover the Bootrec operations and their limits.
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Use BCDBoot when system-partition boot files need rebuilding
BCDBoot is a distinct option for recreating boot files on the system partition using files from the installed Windows directory. First identify the volumes in WinRE Command Prompt:
diskpart
list vol
exitFind the volume containing the Windows directory and identify the system partition. Microsoft’s example command is:
bcdboot D:WindowsD: is only an example; use the drive letter that actually contains the offline Windows directory. BCDBoot’s behavior depends on whether the PC boots using BIOS or UEFI, including how the system partition and UEFI firmware entries are handled. Check the machine’s boot mode and partition layout before using it. See Microsoft’s BCDBoot command-line options for the documented behavior.
Choose the repair by the symptom
| Recovery method | Best fit | Key limitation |
|---|---|---|
| Startup Repair | First attempt for common startup problems, including damaged MBR or BCD | It may not resolve the fault; review the repair result and available log if it fails. |
bootrec /fixmbr |
Suspected damaged master boot code | Does not repair partition-table corruption. |
bootrec /fixboot |
Damaged boot-sector code | Targets a different component from MBR boot code. |
| Bootrec BCD sequence | BCD-related startup error | Must use the correct offline Windows and boot-file paths. |
| BCDBoot | Missing or damaged system-partition boot files or BCD store | Requires the correct Windows directory, system partition, and firmware context. |
When to stop and escalate
If Startup Repair and the command appropriate to the symptom do not restore startup, do not try unrelated commands or format a partition as a generic next step. A failed /fixmbr attempt does not show that the partition table is intact; nor does a boot error prove that rewriting it is appropriate. Stop if the disk shows signs of failure, the partition layout is unclear, or you cannot confidently identify the Windows and system volumes. At that point, diagnosis and preserving data should come before further changes to the disk.
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