How Can You Fix Windows 11 Boot Failures After December 2025 and February 2026 Updates?

What Steps Resolve UNMOUNTABLE_BOOT_VOLUME Errors on Windows 11 24H2 and 25H2 Systems?

Understanding the Boot Problem

Windows 11 systems running versions 24H2 and 25H2 experienced critical boot failures following the January 2026 security update KB5074109, released on January 13, 2026. Affected computers displayed an “UNMOUNTABLE_BOOT_VOLUME” error with Stop Code 0xED, preventing system startup entirely. Microsoft traced the root cause to failed December 2025 security updates that left systems in an unstable state during automatic rollback.

The February 2026 update KB5077181 addresses the underlying bug preventing new systems from experiencing this issue. However, systems already experiencing boot failures require manual intervention to restore functionality.​

Systems Already Failing to Boot

For devices displaying the boot volume error, Microsoft recommends business administrators contact technical support. Systems with corrupted Boot Configuration Data (BCD) records or missing Secure Boot entries need specialized recovery procedures beyond standard troubleshooting methods.​

An IT professional recently shared a comprehensive repair solution for recovering non-booting systems, particularly those with UEFI BIOS configurations using GPT partitioning rather than legacy MBR structures.

Pre-Repair Requirements

Before attempting repairs, gather these essential items:

• BIOS access credentials (administrator password if security is enabled)
• Windows 11 bootable installation media on USB 2.0 drive (created using tools like Rufus)
• BitLocker recovery key for encrypted drives
• External storage device for backing up critical files

Critical Warning: Hard drive repair procedures carry inherent risks of complete data loss. Always maintain current backups of important files before proceeding with system-level modifications.

Accessing Windows Recovery Environment

Begin by entering your system’s BIOS setup utility—consult your device manufacturer’s documentation for the specific function key required during startup. Disable Secure Boot within BIOS settings, save the configuration changes, and restart.

Insert your Windows 11 installation USB drive and boot from it by manually selecting the boot device (typically using F12 during startup). Select “Repair computer” rather than installation options, then navigate through Troubleshoot > Advanced Options > Command Prompt.

The system will request your BitLocker recovery key to access encrypted drives. Enter this key to proceed to the command prompt interface at X:\Windows\System32.

Backing Up Critical Data

Before modifying boot configurations, use the command prompt to copy essential files from your non-booting drive to external storage. Navigate to user directories (typically c:\users\USERNAME) and transfer documents, photos, and other irreplaceable data to a connected backup device.

Repairing EFI Boot Configuration

The GPT partition structure requires specific commands for EFI bootloader repair. Legacy bootsect commands apply only to MBR systems and will not resolve UEFI-based boot problems.

Enter diskpart utility and select your primary disk (typically disk 0). List volumes to identify the EFI System Partition—this small FAT32-formatted partition manages boot operations. Assign an unused drive letter to this partition for modification access, then exit diskpart.

Navigate to the EFI boot directory using your assigned drive letter, accessing the path: [drive letter]:\EFI\Microsoft\Boot. Execute the bootrec /FixBoot command to repair boot sector information.

Rebuilding Boot Configuration Data

When standard boot repair fails, rebuild the BCD store completely. First, create a backup of existing boot configuration by renaming the BCD file to BCD.bak or BCD.OLD using the ren command.

Recreate the boot configuration using the bcdboot command, specifying your Windows installation drive (typically c:\Windows), your boot partition drive letter, and the /f ALL parameter to create entries for all firmware types. For systems in Germany or other locales, include the appropriate language code parameter (/l en-DE for German systems).

Execute bootrec /rebuildbcd to scan for Windows installations and add them to the newly created boot configuration. Remove your installation USB drive and restart the system.

Post-Repair Boot Process

During the initial restart, Windows may display an automatic repair menu. Select the automatic repair option and confirm. The system will show “Updates are being performed” through multiple restart cycles.

Eventually, Windows will load successfully. Sign in to your Microsoft 365 account and ENTRA ID, confirming device registration with your organization. Additional authentication through Microsoft Authenticator may be required. Repeat login confirmation for OneDrive, Office 365, and Teams if your organization uses these services.

Important: Do not manually check for Windows updates immediately after recovery. Allow the system to stabilize for 5-10 minutes before restarting.

Re-Enabling Secure Boot

After the initial restart and subsequent 5-10 minute stabilization period, shut down the system completely. Enter BIOS setup again and re-enable Secure Boot, saving the configuration before restarting.

Leave Windows running for 20-30 minutes after startup. The system will automatically detect and download available updates. Allow these downloads to complete fully before installing them individually rather than as a batch.

Recovery Timeline Expectations

The complete recovery process requires patience and careful attention to each stage. Systems typically require several restart cycles and extended idle periods for Windows to stabilize and reconfigure itself properly. Rushing through updates or skipping stabilization periods may reintroduce boot problems.

This reader-contributed solution offers IT professionals and advanced users a pathway to recover systems without performing complete Windows reinstallations, saving significant time and preserving installed applications and configurations.