Fix UNMOUNTABLE_BOOT_VOLUME Error Without Losing Your Files

The UNMOUNTABLE_BOOT_VOLUME error means Windows cannot read or mount the partition that contains its system files, so it cannot start. The usual causes are file-system damage, a failing SSD or hard drive, a loose connection, or a recent Windows change. Use Windows Recovery Environment and the least destructive repairs first; do not format or reinstall Windows until your files are safe and the storage device has been checked.

What the UNMOUNTABLE_BOOT_VOLUME screen is telling you

UNMOUNTABLE_BOOT_VOLUME

Windows shows this blue screen when it cannot mount the volume needed to start the operating system. The volume may be inaccessible because its file-system metadata is damaged, the storage device is failing, the drive connection is unreliable, or Windows received a change it cannot load correctly.

A single occurrence after a forced shutdown or failed update often points to a repairable file-system or startup problem. Repeated blue screens, increasing startup failures, files that suddenly disappear, very slow access, or unusual clicking and grinding from a hard drive point more strongly to hardware failure. SSDs usually do not make mechanical noises, but they can still fail or stop being detected.

Your personal files are not automatically erased by this error. The initial repair tools normally change file-system or startup information rather than your documents, but every repair attempt writes to the disk. If the drive is making unusual noises, disconnecting, or becoming less readable, stop repeated repairs and copy important files first. Do not format the volume, delete partitions, or choose a reset option while your files are still at risk.

Can you fix it without reinstalling Windows?

Usually, yes. A damaged file system, interrupted update, or broken boot configuration can often be repaired from Windows Recovery Environment without reinstalling Windows. A reinstall will not fix a storage device that is physically failing, and it can make later data recovery harder.

This procedure applies mainly to Windows 10 and Windows 11 PCs. You need access to the recovery tools and, for Command Prompt repairs, an account with Administrator privileges. Some recovery actions restart the computer; System Restore and update removal can also change installed software or system files. If Windows starts at any point, back up important files before continuing.

Before repairing, do these checks:

• Disconnect USB drives, memory cards, docking stations, external disks, and other nonessential peripherals. Leave the keyboard, mouse, display, and power connected.
• If the computer reaches recovery options, check whether the internal drive and its Windows partition appear. If the drive is missing from firmware setup or recovery tools, suspect a connection or hardware problem rather than a simple boot-record problem.
• Consider what changed immediately before the failure: a Windows update, forced shutdown, new storage driver, disk movement, or repeated crashes. That clue helps identify the least disruptive repair.

On a desktop, turn the computer off before checking that the SATA data and power cables are firmly seated. On a laptop, do not open the case unless you are comfortable with its service procedure and the device is powered off and disconnected from power.

Use Windows Recovery Environment and work through repairs in this order

Windows normally enters Windows Recovery Environment after several interrupted starts. If it does not, turn the PC on and interrupt startup by holding the power button as Windows begins loading; repeat this only until the recovery screen appears. Repeated forced shutdowns are not a repair and can worsen file-system damage.

If recovery does not appear, create Windows installation media on another working PC using Microsoft’s official Windows media-creation process. Boot the affected computer from that USB drive, select your language, and choose Repair your computer, not Install now. You may need to use the PC’s boot-menu key or change the boot order in firmware settings.

1. Select Troubleshoot and then Advanced options.
2. Run Startup Repair first. It checks common startup files and configuration problems and may restart the computer automatically. If Windows starts, do not immediately run more repairs. First copy important files and check the drive.
3. If Startup Repair fails, return to Advanced options and try System Restore if a restore point exists. Choose a restore point from before the error began. System Restore normally keeps personal files, but it can remove drivers, updates, or applications installed after that point.
4. If the failure followed a Windows update, choose Uninstall Updates. Try the option for the latest quality update first. If that does not help and the option is available, consider removing the latest feature update. This option is not present on every system.
5. Try Startup Settings and choose Safe Mode when it is available. If Safe Mode starts, copy your files and remove a recently installed storage driver or application through Windows settings. Safe Mode may not start when the system partition itself cannot be mounted, so its absence does not prove the drive has failed.
6. From Advanced options, open Command Prompt. Recovery may assign Windows a different drive letter than it uses during normal operation. Identify the Windows partition before running commands. Test likely letters by listing their contents:

dir C:\Windows
dir D:\Windows
dir E:\Windows

Use the letter that contains the Windows directory. In the commands below, D: is an example; replace it with the correct letter.

7. Check and repair the file system. This command can take a long time, especially on a large hard drive. Do not interrupt it just because progress appears slow.

chkdsk D: /f

A successful run reports that Windows made corrections or found no problems. The exact message varies. If it reports unreadable sectors, repeated corruption, an inability to lock the volume, or that the drive is becoming inaccessible, treat that as a reason to prioritize data recovery and hardware diagnosis. The /r option performs a much deeper scan and reads the disk extensively; use it only after considering the condition of the drive and the value of the data.

8. If the file system is repaired but Windows still does not boot, rebuild the boot files. First identify the small system partition with diskpart:

diskpart
list volume
exit

On a UEFI computer, the EFI system partition is usually a small FAT32 volume. Assign it a temporary letter in DiskPart if it has none, then use bcdboot to recreate the startup files. For example, if Windows is D: and the EFI partition is S::

bcdboot D:\Windows /s S: /f UEFI

The expected result is a message that boot files were successfully created. If the command cannot copy boot files, you may have selected the wrong Windows or system partition, or the storage device may be damaged.

On older BIOS-based installations, you may instead use the following commands after confirming the correct Windows and system partitions:

bootrec /fixmbr
bootrec /rebuildbcd

bootrec /fixmbr changes the master boot record and does not format personal data. bootrec /rebuildbcd may find an installed Windows copy and ask whether to add it. Do not use commands that remove partitions or format the disk as a first response.

9. Close Command Prompt and choose Continue to attempt a normal start. If a command reports that the disk is not accessible, disappears from list volume, or produces new read errors, stop escalating repairs. The priority has changed from boot repair to preserving data.

How to tell whether the repair actually worked

A successful restart is only the first check. Sign in normally, open several personal files from different folders, and launch the applications you need. A system that reaches the desktop but freezes, produces read errors, or loses files is not repaired reliably.

Restart from Windows, then perform a full shutdown and cold start. Confirm that the computer starts both times without entering recovery. If the error returns after another shutdown or update, suspect an underlying disk or connection problem rather than assuming the first repair was permanent.

Once Windows is running, review the drive’s reported health with the manufacturer’s diagnostic utility or a trusted disk-health tool. Windows may also expose basic status under the drive’s properties, but a clean status there does not prove that a failing drive is healthy. Look for warnings, rapidly worsening health indicators, read errors, or the drive disappearing from the system.

You can also check the system log for storage-related errors in Event Viewer:

Event Viewer > Windows Logs > System

Search around the failure time for disk, Ntfs, storahci, or storage-controller errors. One log entry is not conclusive, but repeated errors that coincide with freezes or missing files deserve attention. Keep a current backup even if Windows now starts normally.

What to do if every repair fails

Stop running repair commands when the drive repeatedly disconnects, reports unreadable sectors, produces new corruption, or is not detected consistently. Repeated chkdsk runs and boot repairs cannot restore a physically failing device and may reduce the chance of recovering files.

If the drive is still readable, copy important files to another disk before attempting a replacement or reinstall. If Windows will not start, use a Windows installation USB, a recovery environment, or another computer to copy files. If the drive is unstable, copy the most valuable files first and avoid opening large folders repeatedly. A specialist data-recovery service may be appropriate when the files cannot be replaced; do not freeze, heat, strike, or repeatedly power-cycle the drive.

On a desktop, power the computer off and reseat the drive’s data and power cables. Try a known-good SATA cable or another motherboard port if the drive is detected intermittently. For an M.2 SSD, confirm that it is firmly installed and supported by the slot. If the drive is absent from firmware setup, Windows recovery cannot repair it; replace or diagnose the hardware first.

Only reinstall Windows after your files are backed up and the replacement or existing storage device passes its health checks. If the original drive is failing, install Windows on a new drive rather than reinstalling onto the suspect one. Afterward, restore files from backup and install current chipset and storage drivers from the computer or motherboard manufacturer.

To reduce the chance of a repeat, keep regular backups, leave free space on the system drive, install firmware and driver updates from reputable sources, and investigate freezes or file-system warnings instead of repeatedly forcing the PC off. A surge protector or reliable power source can also reduce shutdown-related corruption, but it cannot prevent normal drive wear.

Conclusion

If the repairs do not restore a stable start, stop running commands and protect your files. Check whether the drive is detected and healthy; replace it before reinstalling Windows if its condition is questionable. After Windows starts reliably through both a restart and a cold boot, keep a current backup.

Frequently Asked Questions

Will UNMOUNTABLE_BOOT_VOLUME delete my files?

The error itself does not delete personal files, and the initial recovery tools normally do not format the drive. File loss can still occur if the storage device is failing or if you choose reset, format, or partition commands. Back up readable files before extensive repairs.

Should I run chkdsk with the /r option immediately?

No. Start with `chkdsk D: /f` after confirming the correct Windows drive letter. `/r` performs a much deeper read of the disk and can place additional stress on a failing drive; use it only when the drive appears stable and your data is protected.

Why does the Windows drive have a different letter in Recovery Environment?

Recovery Environment assigns drive letters independently from normal Windows. The Windows partition may be `D:` or another letter instead of `C:`, so check for the directory containing `Windows` before running `chkdsk`, `bcdboot`, or other commands.