Unmountable Boot Volume: Fix the BSOD

Updated 13 November 2026 · Standard formula, shown below

If you see the Unmountable Boot Volume blue screen error, your Windows PC cannot read the drive that holds the operating system, so it stops booting. This guide explains what causes it and walks you through the most effective fixes, from automatic startup repair to manual command-line checks.

What Is the Unmountable Boot Volume Error?

Unmountable Boot Volume is a Windows stop code (0x000000ED) that appears during the boot process when the system cannot mount the boot volume—the partition where Windows is installed. The error is almost always tied to a problem with the storage drive itself, its file system, or the connection between the drive and the motherboard. It is not a sign of a corrupted Windows installation in most cases; it points to the disk not being readable at the hardware or file-system level.

You will typically see the error on a blue screen with the text “UNMOUNTABLE_BOOT_VOLUME” and a note that Windows has been shut down to prevent damage. The screen may appear immediately after the BIOS/UEFI splash screen or after a few seconds of the Windows logo. In some cases, the system will try to run automatic repair and then fail, returning to the same blue screen.

Common Causes and What They Mean

The error has a handful of well-known triggers. Knowing which one you are dealing with helps you choose the right fix.

File system corruption: The NTFS or FAT32 file system on the boot drive has errors, often from sudden power loss, improper shutdown, or bad sectors.
Faulty cable or connection: A loose SATA data cable, a damaged cable, or a failing USB port (for external drives) can make the drive temporarily invisible or unreadable.
Drive hardware failure: The physical hard disk or SSD is failing, with bad sectors or failing controller electronics.
Incorrect BIOS/UEFI settings: The boot mode (Legacy vs. UEFI) or SATA mode (AHCI vs. IDE) may be set incorrectly, or the boot order points to the wrong device.
Driver or firmware issues: Rarely, a recently installed disk driver or a firmware bug on the SSD can cause the mount to fail.

Before You Start: Prepare Your System

Because the error prevents Windows from loading normally, you will need a way to run repair tools. If you have a Windows installation USB drive or a recovery drive, you can boot from it. If you do not have one, you can create one on another working PC using Microsoft’s Media Creation Tool (for Windows 10/11). You will also need to know your Windows version (e.g., Windows 11, Windows 10) because the repair commands are slightly different in older versions like Windows 7.

If your PC is under warranty or you suspect physical drive failure, back up any data you can before running repairs. You can often copy files from the drive by booting from a Linux live USB, but if the drive is failing, do this as soon as possible.

Fix 1: Run Automatic Startup Repair

Windows includes a built-in repair tool that can fix common boot issues, including file system errors. To run it:

Boot from your Windows installation USB or recovery drive.
Choose your language and click Next.
Click Repair your computer (bottom-left corner).
Select Troubleshoot > Advanced options > Startup Repair.
Wait for the process to finish. It may take several minutes and may restart the PC.

If Startup Repair says it could not fix the problem, move on to the next step. It often fails when the issue is deeper than a simple boot configuration error.

Fix 2: Run CHKDSK from the Command Prompt

The most direct fix for file system corruption is the Check Disk utility (chkdsk). It scans the drive for errors and repairs them. You run it from the Command Prompt in the recovery environment.

Boot from your installation media and go to Troubleshoot > Advanced options > Command Prompt.
Type chkdsk /f /r and press Enter.
If prompted to dismount the volume, type Y and press Enter.
Wait for the scan to complete. It can take a long time on large drives.
Type exit and restart the PC normally.

The /f flag fixes errors, and /r locates bad sectors and recovers readable information. If you know the boot drive letter (often C:, but in the recovery environment it may be D: or another letter), you can specify it, e.g., chkdsk D: /f /r. If you are unsure, type diskpart, then list volume to see the drive letters, then exit.

Fix 3: Check and Repair the Boot Configuration

If chkdsk finds no errors, the boot configuration data (BCD) may be corrupted. This is less common with the Unmountable Boot Volume error, but worth trying.

Open Command Prompt as above.
Type bootrec /fixmbr and press Enter.
Type bootrec /fixboot and press Enter. If you get “Access is denied,” type bootrec /rebuildbcd instead.
Type exit and restart.

These commands rewrite the master boot record and the boot sector. They do not touch your personal files.

Fix 4: Check Hardware Connections and BIOS Settings

If software repairs do not work, the problem may be physical or in the system firmware.

Reseat cables: For desktop PCs, open the case and unplug/replug the SATA data and power cables to the boot drive. For laptops, reseat the drive if it is user-accessible.
Try a different port: Move the SATA cable to another motherboard port, or use a different USB port for an external drive.
Check BIOS/UEFI: Enter the BIOS (usually by pressing Del, F2, or F12 during startup). Verify that the boot drive is detected and that the boot order lists it first. For SSDs, ensure the SATA mode is set to AHCI (not IDE) unless you are sure your Windows installation was made in IDE mode.

Fix 5: Use System Restore or Reset

If the error started after a recent driver or system change, System Restore can roll back to a working state. From the recovery environment, go to Troubleshoot > Advanced options > System Restore. Choose a restore point from before the problem began. If no restore points exist, you may need to reset Windows, which removes apps and settings but can keep your personal files. Choose Reset this PC from the recovery menu and follow the prompts.

Frequently Asked Questions

Can I recover my files before fixing the error?

Yes, if the drive is still physically readable. Boot from a Linux live USB (like Ubuntu) and copy your files to an external drive. Alternatively, you can use a Windows recovery drive and access the command prompt to copy files manually, but Linux is often easier for browsing the drive.

Will chkdsk delete my files?

No, chkdsk does not delete files. It repairs file system metadata and can move data from bad sectors to good ones. In rare cases, if a file is severely corrupted, it may be unrecoverable, but chkdsk does not intentionally remove your data.

What if the error appears after a Windows update?

Try System Restore to a point before the update. If that fails, run chkdsk /f and then try Startup Repair. Some updates change disk driver settings, so also check the SATA mode in BIOS.

Is this error a sign that my hard drive is dead?

Not necessarily. It can be a loose cable or a file system issue. However, if chkdsk finds many bad sectors or the drive makes clicking noises, the drive may be failing. Back up data immediately and consider replacing the drive.

Can I fix this without a Windows installation USB?

Sometimes. If the error appears after a sudden power loss, restarting the PC a few times may trigger automatic repair. If that does not work, you will need external media to run the repair tools. You can create a recovery drive on another PC.

Will resetting Windows fix the error?

It can, if the problem is software-based. However, if the drive has physical damage, resetting may fail or make it worse. Always back up your data first.

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