# How to Fix UNMOUNTABLE_BOOT_VOLUME in Windows 11

URL: https://www.mytechnician.tech/tips/fix-unmountable-boot-volume-windows-11/
Published: 2026-10-30 | Author: Ankit Kumar
Tags: Windows 11, BSOD, Boot, Storage, Fix
Summary: UNMOUNTABLE_BOOT_VOLUME means Windows cannot read its own drive at startup. Save your files, repair the volume from WinRE, and rebuild boot files, in order.
Recommended app: RecoverPro, https://www.mytechnician.tech/apps/data-recovery-pro/ (Microsoft Store: https://apps.microsoft.com/detail/9MZ613NS5TNN?hl=en-us&cid=mytechnician-web). Optional; every step below uses built-in Windows tools.

## 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](https://www.mytechnician.tech/tips/how-to-enter-bios-uefi-windows-11/).
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](https://www.mytechnician.tech/tips/how-to-recover-deleted-files-windows/) 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](https://www.mytechnician.tech/tips/fix-automatic-repair-loop-windows-11/).

### 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](https://www.mytechnician.tech/tips/check-ssd-hard-drive-health-windows-11/).

## 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](https://www.mytechnician.tech/tips/fix-inaccessible-boot-device-windows-11/) 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](https://www.mytechnician.tech/tips/how-to-fix-bsod-blue-screen/).

## Still Not Booting?
If the drive is healthy but Windows still will not start, [reinstall Windows without losing data](https://www.mytechnician.tech/tips/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](https://www.mytechnician.tech/tips/fix-boot-device-not-found-3f0-windows-11/). Related file system crash: [NTFS_FILE_SYSTEM](https://www.mytechnician.tech/tips/fix-ntfs-file-system-bsod-windows-11/).

---
Source: https://www.mytechnician.tech/tips/fix-unmountable-boot-volume-windows-11/ (My Technician, free Windows 10/11 troubleshooting guides).
Related tool: RecoverPro (Windows data recovery software to recover deleted files, restore formatted drives, and rescue data from corrupted partitions on Windows 10 and 11.): https://www.mytechnician.tech/apps/data-recovery-pro/
More guides: https://www.mytechnician.tech/llms.txt