The UNMOUNTABLE_BOOT_VOLUME error usually means Windows 10 can’t access the drive or partition where the operating system is installed. Because the required startup files aren’t available, Windows stops loading and displays the Blue Screen of Death. Mostly, this BSOD displays after an unexpected shutdown or a power outage that interrupts disk operations. A corrupted file system, damaged boot files, disk errors, or a failing SSD or hard drive are among the most common reasons for this. In this article, you’ll learn what causes the UNMOUNTABLE_BOOT_VOLUME error in Windows 10, and solutions to repair the boot volume and start your PC normally again.
Why Does the UNMOUNTABLE_BOOT_VOLUME Error Occur in Windows 10?
Windows 10 displays the UNMOUNTABLE_BOOT_VOLUME error when it cannot load the partition that contains the files needed to start the operating system. This usually happens because the boot volume has become inaccessible or damaged.
The most common reasons include:
- The file system is corrupted. If Windows cannot read the NTFS file system on the boot partition, startup stops, and the blue screen appears.
- The hard drive has developed bad sectors. Many Windows 10 PCs still use traditional hard drives. As they age, bad sectors can prevent Windows from reading critical startup files.
- Boot files are damaged or missing. Power failures, interrupted updates, or disk errors can corrupt the Boot Configuration Data (BCD) or other files required during startup.
- The computer shut down unexpectedly. Losing power while Windows is writing data to the disk can damage the file system and trigger boot problems.
- The BIOS storage mode has changed. Switching from AHCI to IDE or RAID (or vice versa) without reinstalling Windows can prevent the operating system from accessing the boot drive.
- Loose SATA cables or hardware problems. On desktop PCs, a loose SATA data or power cable can interrupt communication between Windows and the storage drive.
Before trying advanced repairs, think about what happened just before the error appeared. If it started after a Windows update, a repair tool may fix it. If it followed weeks of slow performance or disk-related warnings, checking the health of your hard drive should be your priority.
1. Run Startup Repair
If the UNMOUNTABLE_BOOT_VOLUME error displays suddenly and Windows won’t start, start with Startup Repair. It can automatically fix common boot problems without affecting your personal files.
How to run Startup Repair
- Turn on your PC. When the Windows logo appears, press and hold the Power button until the PC shuts down.
- Repeat this process 2–3 times until Preparing Automatic Repair appears.
- Select Advanced options.
- Go to Troubleshoot > Advanced options > Startup Repair.
- Select your Windows 10 account and enter your password if prompted.
- Wait while Windows scans for startup problems and applies any available repairs.
- Restart your computer.
If Startup Repair doesn’t resolve the UNMOUNTABLE_BOOT_VOLUME error, the boot drive may contain file system errors. In the next step, you’ll use CHKDSK to scan and repair the drive.
2. Check the Boot Drive for Disk Errors Using CHKDSK
If Startup Repair couldn’t fix the problem, the next step is to check the boot drive for file system errors and bad sectors. Windows includes the CHKDSK (Check Disk) utility, which can repair logical disk errors and recover readable data from damaged sectors.
Run CHKDSK from Windows Recovery Environment
- Boot into Windows Recovery Environment (WinRE).
- Select Troubleshoot > Advanced options > Command Prompt.
- At the Command Prompt, type the following command and press Enter:
chkdsk C: /f /r
If Windows is installed on another drive, replace C: with the correct drive letter.
What the command does
- /f repairs file system errors.
- /r locates bad sectors and attempts to recover readable data.
The scan may take anywhere from a few minutes to several hours, depending on your drive size and the number of errors found. Do not interrupt the process.
Once the scan finishes, close Command Prompt and restart your computer.
If CHKDSK reports a large number of bad sectors or continues finding new errors every time you run it, your hard drive may be failing. Back up your files as soon as possible and consider replacing the drive.
If the disk check doesn’t resolve the error, some Windows system files may be corrupted. The next step is to scan and repair them using SFC and DISM.
3. Repair Corrupted Windows System Files
Sometimes the boot drive is healthy, but Windows still won’t start because essential system files have been damaged or deleted. Running System File Checker (SFC) and Deployment Image Servicing and Management (DISM) can repair these files.
Run System File Checker
- Open Command Prompt from Windows Recovery Environment (WinRE).
- Enter the following command and press Enter:
sfc /scannow /offbootdir=C:\ /offwindir=C:\Windows
Replace C: if your Windows installation uses a different drive letter in WinRE.
Wait for the scan to complete. If SFC finds corrupted files, it will attempt to repair them automatically.
Run DISM (if SFC cannot repair the files)
If SFC reports that it found corrupted files but couldn’t fix them, run the following command:
DISM /Image:C:\ /Cleanup-Image /RestoreHealth
After DISM finishes, run the SFC command again to verify that all corrupted system files have been repaired.
Restart your computer and check whether Windows boots normally.
If repairing the Windows system files doesn’t help, the boot configuration itself may be damaged. Next, rebuild the Windows boot files and BCD.
4. Rebuild the Boot Configuration Data (BCD)
If Windows system files are intact but your PC still won’t start, the boot configuration may be damaged. Rebuilding the Boot Configuration Data (BCD) can help Windows locate the operating system and boot correctly.
Rebuild the BCD
- Boot into Windows Recovery Environment (WinRE).
- Open Command Prompt from Advanced options.
- Run the following commands one at a time, pressing Enter after each:
bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd
If Windows installation is found, type Y to add it to the boot list.
If you receive “Access is denied”
On some Windows 10 systems, the bootrec /fixboot command may display an Access is denied error. If that happens, you can rebuild the EFI boot files using the BCDBoot command instead.
bcdboot C:\Windows
Replace C: with the correct Windows drive letter if necessary.
Restart your computer after the commands finish.
If Windows still fails to boot, the problem may have started after a recent update or system change. Restoring Windows to an earlier working state is the next thing to try.
5. Restore Windows to an Earlier Working State
If the error started after installing a driver, software, or Windows update, System Restore may return your computer to a previous working state without affecting your personal files.
Note: This option only works if System Restore was enabled before the problem occurred.
Use System Restore
- Start your PC in Windows Recovery Environment (WinRE).
- Select Troubleshoot > Advanced options > System Restore.
- Choose your Windows 10 account and enter the password if prompted.
- Select a restore point created before the UNMOUNTABLE_BOOT_VOLUME error started.
- Click Next > Finish and wait for Windows to restore the system.
Your computer will restart automatically after the restore process is complete.
If restoring Windows doesn’t fix the startup problem, the issue may be related to a recently installed update. Removing that update is worth trying before considering more advanced recovery options.
6. Uninstall the Latest Windows Update
If the UNMOUNTABLE_BOOT_VOLUME error appeared immediately after installing a Windows update, removing that update may restore your PC to a working state.
Remove the latest quality update
- Boot into Windows Recovery Environment (WinRE).
- Select Troubleshoot > Advanced options > Uninstall Updates.
- Choose Uninstall latest quality update.
- Follow the on-screen instructions and restart your computer.
If the problem started after a major Windows 10 feature update, choose Uninstall latest feature update instead.
Tip: After Windows starts normally, pause updates for a few days until Microsoft releases a fix if the issue was caused by a faulty update.
If uninstalling the update doesn’t help, it’s time to check whether the problem is related to the storage drive itself.
7. Check if Your Hard Drive or SSD Is Failing
If none of the previous fixes work, the problem may be with the storage drive itself. A failing hard drive or SSD can prevent Windows 10 from accessing the boot partition, causing the UNMOUNTABLE_BOOT_VOLUME error.
Common signs of a failing drive include:
- Frequent Blue Screen errors
- Unusually slow startup
- Clicking or grinding noises (HDDs)
- File corruption or missing files
- SMART health warnings
If you can access the drive from another computer, check its health using a SMART monitoring tool. If the drive reports hardware errors or continues developing bad sectors, replace it as soon as possible to avoid data loss.
Tip: If your drive is healthy, continue with the final solution before considering a clean installation of Windows.
8. Reset or Reinstall Windows 10
If you’ve tried all the previous fixes and your PC still won’t boot, the Windows installation may be too damaged to repair. Resetting or reinstalling Windows is usually the last option.
Reset Windows 10
- Boot into Windows Recovery Environment (WinRE).
- Select Troubleshoot > Reset this PC.
- Choose Keep my files if you want to preserve your personal data.
- Follow the on-screen instructions to complete the reset.
If Windows still won’t start or the reset process fails, perform a clean installation of Windows 10 using a bootable USB drive.
Important: If you suspect your hard drive or SSD is failing, replace it before reinstalling Windows. Installing Windows on a failing drive is unlikely to fix the problem and may lead to data loss.
Frequently Asked Questions
This error means Windows 10 cannot access the boot partition that contains the files required to start the operating system. As a result, Windows stops loading and displays a Blue Screen of Death (BSOD).
Yes. A failing hard drive or SSD can make the boot partition inaccessible, preventing Windows from loading normally. If your computer has also become slow, freezes frequently, or makes unusual noises (HDDs), check the drive’s health.
Not necessarily. Most repair methods, including Startup Repair, CHKDSK, System Restore, and rebuilding the boot configuration, do not delete your personal files. However, you should back up important data if the storage drive is failing.
In many cases, yes. Running Startup Repair, repairing the file system with CHKDSK, fixing corrupted system files, or rebuilding the boot configuration is often enough to restore Windows.
If the error continues after trying all the solutions, test the health of your hard drive or SSD. If the drive is healthy, resetting or reinstalling Windows 10 may be the only remaining option.
