How to Fix UNMOUNTABLE_BOOT_VOLUME in Windows 11

•
By My Technician Editorial Team · Edited by Ankit Kumar
Windows 11BSODBootStorageFix
On this page

The Problem

The PC blue-screens during startup with UNMOUNTABLE_BOOT_VOLUME (stop code 0x000000ED), often in a loop. Windows found the drive it boots from but could not mount the file system on it.

There are four usual causes, roughly in order of likelihood:

  1. File system damage on the Windows drive after a power cut, forced shutdown, or interrupted update.
  2. A storage controller change in the BIOS, such as switching SATA mode between AHCI and RAID, or toggling Intel VMD.
  3. A failing SSD or hard drive, or a loose cable on a desktop.
  4. Damaged boot configuration after a failed update or a dual-boot setup.

Before anything else: your files may be at risk. If the drive is failing, every repair attempt puts more wear on it. Step 1 covers copying your files off first.

Symptoms

  • Blue screen reading UNMOUNTABLE_BOOT_VOLUME a few seconds after the Windows logo.
  • The PC restarts into Automatic Repair, which reports it could not repair your PC.
  • It started right after a BIOS update, a BIOS settings change, or moving the drive to another PC.
  • Clicking or grinding sounds from a hard drive, or the drive disappearing from the BIOS.

Quick Checks

  1. Undo recent BIOS changes. If you changed SATA mode, RAID, Intel VMD, or reset the BIOS to defaults, set it back to how it was. Windows only loads the storage driver for the mode it was installed with. See how to enter BIOS/UEFI.
  2. Reseat cables on a desktop. Unplug power, then reseat the SATA data and power cables (or the M.2 drive) and try again.
  3. Unplug USB drives and memory cards, then boot again.

The Fix: Step-by-Step

Step 1: Copy Your Files Off First

  1. Boot from a Windows 11 installation USB (make one on another PC with Microsoft's Media Creation Tool).
  2. On the setup screen, choose Next → Repair your computer → Troubleshoot → Command Prompt.
  3. Find your drive letters. They are often different from normal in this environment: 
    diskpart
list volume
exit
    Look for the large NTFS volume; that is usually your Windows drive, often shown as D: here.
  4. Copy your user folder to an external drive (replace the letters and name with yours): 
    robocopy D:\Users\YourName E:\Backup /E /R:1 /W:1

If the Windows volume will not open at all, remove the drive and connect it to another PC with a USB adapter to copy the files, or see recover deleted files for recovery options.

Step 2: Run Startup Repair

From the same Troubleshoot menu, choose Advanced options → Startup Repair. Let it run once. It fixes simple boot configuration and file system problems automatically.

If you are caught in a repair loop, see fix the Automatic Repair loop.

Step 3: Repair the File System With CHKDSK

  1. Open Command Prompt from the recovery environment again.
  2. Run CHKDSK on the Windows volume, using the letter you found in Step 1: 
    chkdsk D: /f
  3. If it reports bad sectors or cannot finish, run the deeper scan: 
    chkdsk D: /r

/r can take hours on a large hard drive. Leave it running. If the drive is protected by BitLocker, unlock it first with manage-bde -unlock D: -RecoveryPassword <your 48-digit key>. The key is at aka.ms/myrecoverykey on another device.

Step 4: Rebuild the Boot Files

If CHKDSK finished but Windows still will not start:

  1. Run: 
    bcdboot D:\Windows
    This rewrites the boot files to the system partition. On most UEFI PCs, this is all you need.
  2. If that does not help, try: 
    bootrec /fixmbr
bootrec /rebuildbcd

bootrec /fixboot often returns Access is denied on UEFI systems. That is a known limitation, not a sign your drive is broken: bcdboot does the same job.

Step 5: Uninstall the Last Update

If the error appeared right after Windows Update:

  1. Troubleshoot → Advanced options → Uninstall Updates.
  2. Try Uninstall latest quality update first, then Uninstall latest feature update if that does not help.

Step 6: Check the Drive's Health

If CHKDSK found bad sectors, or the error keeps returning, the drive may be failing. Connect it to another PC and check its SMART data with CrystalDiskInfo. A Caution or Bad status means replace the drive. See check SSD or hard drive health.

What Not to Do

  • Don't run chkdsk /r repeatedly on a drive that is clicking. Copy your files off first: a failing drive may only survive one long scan.
  • Don't reinstall Windows until your files are safely on another drive.
  • Don't change SATA mode to "fix" it unless you know it was changed. Switching it the wrong way causes INACCESSIBLE_BOOT_DEVICE instead.

FAQ

Can UNMOUNTABLE_BOOT_VOLUME be fixed without losing data?

Usually, yes. CHKDSK and boot repair do not erase your files. Data is only lost if the drive itself is failing, which is why you copy files off first.

What is the difference between this and INACCESSIBLE_BOOT_DEVICE?

INACCESSIBLE_BOOT_DEVICE means Windows could not talk to the drive at all, usually a driver or controller problem. UNMOUNTABLE_BOOT_VOLUME means it reached the drive but the file system on it could not be read, usually corruption or a failing drive.

Is the stop code a sign of bad RAM?

Rarely. Faulty RAM can corrupt data written to the drive, so if CHKDSK fixes the drive and the error returns within days, test the memory as described in how to fix a BSOD.

Still Not Booting?

If the drive is healthy but Windows still will not start, reinstall Windows without losing data using the installer USB. If the drive is not listed in the installer at all, see fix boot device not found. Related file system crash: NTFS_FILE_SYSTEM.

Related guides