How to Fix UNMOUNTABLE_BOOT_VOLUME (Windows)
Quick Answer
The UNMOUNTABLE_BOOT_VOLUME error indicates that Windows cannot access the boot volume, which is the partition containing the operating system. This often points to issues with the hard drive, corrupted system files, or incorrect boot configuration. The fastest way to attempt a fix is to restart the computer and access the Windows Recovery Environment to run system utilities.
What Causes This Error
- Corrupted file system on the boot volume.
- Damaged or faulty hard disk drive (HDD) or solid-state drive (SSD).
- Incorrect or corrupted boot configuration data (BCD).
- Loose or faulty data cables connecting the boot drive.
- Outdated or corrupted storage controller drivers.
- Improper shutdown or power loss leading to data corruption.
Step-by-Step Fixes
1Perform a Hard Reboot and Access Advanced Startup Options
- Turn off your computer by pressing and holding the power button for 10 seconds.
- Press the power button again to turn on your computer.
- As soon as you see the Windows logo, press and hold the power button again for 10 seconds to turn off your computer.
- Repeat steps 2 and 3 two more times. On the third restart, allow the computer to boot normally. It should enter the Windows Recovery Environment (WinRE).
- Select 'Troubleshoot' > 'Advanced options' to access further recovery tools.
2Run Check Disk Utility (chkdsk) to Fix UNMOUNTABLE_BOOT_VOLUME
- From the 'Advanced options' screen (accessed via hard reboot), select 'Command Prompt'.
- Type 'chkdsk c: /f /r /x' and press Enter. Replace 'c:' with the correct drive letter of your Windows installation if it's different (often 'D:' or 'E:' in WinRE).
- Allow the utility to complete the scan and repair process. This may take a significant amount of time depending on the drive size and extent of corruption.
- After 'chkdsk' finishes, type 'exit' and press Enter.
- Select 'Continue' to exit WinRE and restart your computer, checking if the error is resolved.
3Repair Boot Configuration Data (BCD)
- From the 'Advanced options' screen, select 'Command Prompt'.
- Type 'bootrec /fixmbr' and press Enter.
- Type 'bootrec /fixboot' and press Enter. If access is denied, proceed to the next step.
- Type 'bootrec /rebuildbcd' and press Enter.
- If prompted to add installation to boot list, type 'Y' and press Enter. Type 'exit' and restart your computer.
4Run System File Checker (SFC)
- From the 'Advanced options' screen, select 'Command Prompt'.
- Type 'sfc /scannow' and press Enter.
- Wait for the scan to complete. This utility will attempt to find and repair corrupted Windows system files.
- If SFC reports that it found corrupted files but was unable to fix some of them, you may need to run 'DISM /Online /Cleanup-Image /RestoreHealth' (if Windows is bootable) or consider a system restore.
- Type 'exit' and press Enter, then restart your computer.
Advanced Fixes
Perform a System Restore
- From the 'Advanced options' screen, select 'System Restore'.
- Follow the on-screen prompts to choose a restore point. Select a restore point from before the error started occurring.
- Confirm your restore point and allow the system restore process to complete. Your computer will restart.
- Do not interrupt the system restore process once it has started.
- After the restart, check if the UNMOUNTABLE_BOOT_VOLUME error is resolved.
Reinstall Windows
- From the 'Advanced options' screen, select 'Reset this PC'.
- Choose either 'Keep my files' or 'Remove everything'. 'Remove everything' provides a cleaner installation but deletes all personal data.
- Follow the on-screen instructions to proceed with the Windows reinstallation.
- Ensure you have a backup of important files if you choose 'Remove everything'.
- After the reinstallation, install necessary drivers and software.
Frequently Asked Questions
What does UNMOUNTABLE_BOOT_VOLUME mean?
The UNMOUNTABLE_BOOT_VOLUME error indicates that your Windows operating system cannot access the partition designated as the boot volume. This volume contains critical system files required for Windows to start. Essentially, the system cannot 'mount' or read the drive it needs to boot from.
Will fixing UNMOUNTABLE_BOOT_VOLUME cause data loss?
Basic troubleshooting steps like 'chkdsk' or 'bootrec' are generally safe and aim to repair without data loss. However, if the underlying cause is severe disk corruption or hardware failure, data loss is a possibility. Performing a 'System Restore' reverts system changes but typically preserves personal files. Reinstalling Windows with the 'Remove everything' option will delete all data.
Can a loose cable cause UNMOUNTABLE_BOOT_VOLUME?
Yes, a loose or faulty data cable connecting your hard drive or SSD to the motherboard can prevent the system from properly detecting or accessing the boot volume, leading to the UNMOUNTABLE_BOOT_VOLUME error. Checking cable connections is a valid initial troubleshooting step if you are comfortable opening your computer case.
How do I know if my hard drive is failing?
Signs of a failing hard drive include frequent UNMOUNTABLE_BOOT_VOLUME errors, slow performance, unusual clicking or grinding noises (for HDDs), files becoming corrupted, or the computer failing to detect the drive at all. If 'chkdsk' reports numerous bad sectors or fails to complete, it may indicate drive failure.