UNMOUNTABLE_BOOT_VOLUME Error: How to Fix It Safely

Windows starts to load, then crashes to a blue screen with the stop code UNMOUNTABLE_BOOT_VOLUME. Restarting brings you right back, or into an Automatic Repair loop. The unmountable boot volume error (bug check 0x000000ED) means Windows found the drive it was booting from but couldn’t mount the file system on it, so it can’t read its own system files.

There are two very different reasons that happens, and they call for opposite approaches. Telling them apart before you run any repair is the most important thing you can do for your data.

What causes an unmountable boot volume

File-system corruption (the drive is fine)

The NTFS structures that describe where files live have become inconsistent. Typical triggers:

• A power outage or forced shutdown during a write.
• An interrupted Windows update.
• A driver problem that wrote bad data to the disk.

In this case the hardware is healthy, and a file-system repair often fixes the error.

A failing drive (the hardware is the problem)

The drive can’t reliably read the sectors that hold the file system. Bad sectors on a hard drive, or a degrading SSD, can make the boot volume unreadable. Here, repair tools are the wrong move: they put hours of heavy reads and writes on hardware that’s already struggling.

Signs it’s the drive, not just the file system

Assume hardware failure, and skip the repair steps below, if any of these apply:

• The drive clicks, beeps, grinds, or buzzes.
• The drive isn’t detected in BIOS, or appears only some of the time.
• The PC was slowing down, freezing, or showing disk errors before this happened.
• A SMART tool previously showed reallocated or pending sectors (see Current Pending Sector Count).
• The error came after a drop, spill, or power surge.

Fixes for file-system corruption

These are run from the Windows Recovery Environment (WinRE). Windows usually opens it after two failed boots. If not, boot from a Windows installation USB and choose Repair your computer.

1. Check that the drive is detected

Enter BIOS setup at power-on (usually F2, Del, F10, or Esc) and confirm the drive is listed. If it isn’t, stop and read “If the drive is failing” below.

2. Run Startup Repair

Troubleshoot → Advanced options → Startup Repair. It handles some boot-configuration problems automatically.

3. Run a read-only chkdsk first

Go to Troubleshoot → Advanced options → Command Prompt. WinRE often assigns different drive letters, so find the one holding your Windows folder:

dir C:\
dir D:\

Then check the file system without changing anything:

chkdsk C:

Run with no switches, chkdsk only reports what it finds. If the drive is BitLocker-encrypted, WinRE will ask for the recovery key first. See how to find your BitLocker recovery key.

4. Repair, but only if the drive looks healthy

If the read-only scan finishes normally and reports file-system errors, and you have none of the warning signs above, run:

chkdsk C: /f

/f fixes file-system errors. Many guides go straight to chkdsk /r, which also scans every sector for bad spots. On a healthy drive that’s fine. On a drive that’s starting to fail, it’s hours of stress at exactly the wrong moment. If you’re not sure the hardware is healthy, don’t use /r.

One more caution: chkdsk /f fixes corruption by rewriting file-system records, and badly damaged files or folders can end up orphaned or removed. If the data is irreplaceable, copying your files off first (see “Rescue files before you reinstall” below) is the safer order.

5. Rebuild the boot files

If chkdsk comes back clean but the error remains, rebuild boot files from the same Command Prompt (with the correct letter):

bcdboot C:\Windows

This rewrites boot information only.

6. If chkdsk hangs or reports many errors

A scan that freezes, crawls for hours on one stage, or turns up a long list of errors is a strong sign of failing hardware. Stop it and power down. See Windows stuck repairing disk errors for why letting it run can make things worse.

Rescue files before you reinstall

If repairs don’t work, don’t reset the PC with “Remove everything,” format the drive, or do a clean install while your files are still on it. Copy them off first:

• Connect the drive to another computer with a USB-to-SATA or USB-to-NVMe adapter and copy what you need. You’ll need the BitLocker recovery key if the drive is encrypted.
• If the other PC reports the drive as RAW or asks to format it, don’t. Formatting would overwrite the very structures a recovery needs.
• If the drive is failing, the professional approach is to make a sector-by-sector image first and work from that copy, so the original only has to be read once.

If the drive is failing

If the drive isn’t detected, makes noise, or the read-only chkdsk stalls, stop all repair attempts. Every restart, scan, and recovery program run puts more wear on a drive that may have limited reads left. Power it down and get help.

The bottom line

UNMOUNTABLE_BOOT_VOLUME means Windows can’t mount its own drive. If the cause is file-system corruption on a healthy drive, Startup Repair, a read-only chkdsk, and then chkdsk /f often fix it. If there’s any sign of a failing drive, skip the repairs and get the data imaged first. It’s a close relative of INACCESSIBLE_BOOT_DEVICE, where Windows loses access to the drive rather than its file system.

If the drive has failed, our desktop & PC data recovery service can help. ClearQuote recovers single drives for one flat $1,200 price with free prepaid shipping, and you pay nothing unless we recover your data.