How to Fix UNMOUNTABLE_BOOT_VOLUME BSOD (0x000000ED) on Windows
chkdsk C: /r, then bootrec /fixmbr, bootrec /fixboot, and bootrec /rebuildbcd. Check that the SATA mode in BIOS or UEFI still matches the mode Windows was installed with.What error 0x000000ED means
Error code 0x000000ED carries the stop code name UNMOUNTABLE_BOOT_VOLUME. In plain terms, Windows tried to mount its boot volume — the partition that holds the files Windows needs to start — and could not get access to it. Mounting simply means making a drive partition available for reading, and when that step fails, Windows has nowhere to load its core files from. Rather than start up half-broken, it halts with a blue screen.
This is a boot problem, not a problem inside a running Windows session, which changes how you fix it. You cannot open Settings or Device Manager, because Windows never gets that far. All of the repairs happen from the recovery environment instead: Automatic Repair, Command Prompt from a recovery USB, or the BIOS setup screen. That sounds intimidating, but the tools involved are built into Windows, and none of the early steps touch your personal files.
The error is also different from a missing operating system message. Here Windows found a drive and a partition, but the file system on it is damaged, the boot configuration is pointing at the wrong place, or the drive hardware is no longer responding reliably. Figuring out which of those three is the cause is exactly what the steps below do, in order from the least destructive fix to the most serious diagnosis.
Common causes
- A corrupt file system on the boot volume: a power cut, a forced shutdown, or a crashed update can leave the NTFS file system half-written, so Windows cannot read the partition on the next start.
- Damaged boot configuration data: a failed update, a botched dual-boot change, or a disk-cloning mistake can break the boot records that tell the PC where Windows lives.
- A SATA mode changed in BIOS or UEFI: switching the storage controller between AHCI, RAID, and IDE after Windows is installed leaves Windows loading the wrong storage driver at boot time.
- A failing hard drive or SSD: bad sectors on the boot partition, a worn-out SSD, or a dying mechanical drive that clicks or drops out will make the volume unreadable.
- A bad Windows update or a failing storage cable: an interrupted update can leave boot files inconsistent, and on a desktop PC a loose or damaged SATA cable can make a healthy drive vanish intermittently.
How to fix error 0x000000ED — step by step
Work through these fixes in order. Start with Automatic Repair, because it fixes the simplest cases on its own, and only move to Command Prompt repairs when the PC will not boot far enough to repair itself.
- Let Automatic Repair run first. Power the PC on and let Windows fail to start. After two or three failed starts, Windows 10 and 11 open Automatic Repair on their own. Choose Advanced options, then Troubleshoot, then Startup Repair, and let it finish before you touch anything else. If the PC boots after the repair, you are done; if it returns to the same blue screen, move on to the Command Prompt steps below.
- Open Command Prompt from recovery media. If Automatic Repair does not open, boot from a Windows installation USB, choose your language, click Repair your computer, then go to Troubleshoot, Advanced options, and Command Prompt. From here you can run the disk and boot repairs that need the drive offline. Note that in recovery mode your Windows drive may show up as D: instead of C:, so confirm the drive letter before you run a repair on the wrong volume.
- Run CHKDSK with /r on the boot volume. In Command Prompt, type
chkdsk C: /rand press Enter, replacing C: with your Windows drive letter if recovery assigned a different one. The /r switch finds bad sectors, recovers readable data, and fixes file-system errors that stop Windows from mounting the volume. This scan can take an hour or more on a large drive, so let it finish and do not switch the PC off mid-scan. - Repair the boot records with bootrec. Still in Command Prompt, run
bootrec /fixmbr, thenbootrec /fixboot, thenbootrec /rebuildbcd, pressing Enter after each command. These three commands rewrite the master boot record, write a fresh boot sector, and rebuild the list of Windows installations the PC can start from. If bootrec /fixboot reports Access is denied, runbootsect /nt60 sysfirst and then try bootrec /fixboot again. - Rebuild the boot files with bcdboot if bootrec finds nothing. If bootrec /rebuildbcd reports zero Windows installations, type
bcdboot C:\Windows /s C: /f ALLand press Enter, again swapping C: for your real Windows drive letter. This command copies fresh boot files from your Windows folder onto the system partition. Exit Command Prompt, choose Continue to restart, and see whether Windows boots normally. - Check the SATA mode in BIOS or UEFI. Restart the PC and press the setup key shown on the first screen, usually Delete, F2, or F12, to enter BIOS or UEFI. Find the storage or SATA configuration setting and confirm it matches the mode Windows was installed with, normally AHCI on a modern PC. If someone recently switched it to RAID or IDE, change it back, save with F10, and restart. Changing this setting after Windows is installed is a classic cause of this exact blue screen.
- Uninstall the last update or test the drive itself. If the blue screen began right after a Windows update, go back to Troubleshoot, Advanced options, and choose Uninstall Updates, then remove the latest quality update and restart. If nothing above works, the drive itself may be failing: listen for clicking from a mechanical hard drive, check SMART status from a bootable diagnostic tool, and back up the drive from another PC before you replace it and reinstall Windows.
Did this fix it? Quick checklist
- Windows boots to the login screen without the UNMOUNTABLE_BOOT_VOLUME blue screen
- CHKDSK finishes without reporting unrepairable bad sectors
- bootrec /rebuildbcd finds your Windows installation
- The SATA mode in BIOS or UEFI matches the mode Windows was installed with
If the error persists after all seven steps, stop running repeated scans on the same drive — every failed read attempt pushes a failing drive closer to total failure. If you can still read the drive from another PC, copy anything irreplaceable now, then run the drive maker's own diagnostic, such as Seagate SeaTools, WD Data Lifeguard, or Samsung Magician, for a definitive verdict. If the tool confirms the drive is failing, replace it and do a clean Windows install from freshly made installation media rather than cloning a damaged system onto new hardware.
Frequently asked questions
What does UNMOUNTABLE_BOOT_VOLUME mean?
It means Windows could not mount, or gain access to, the partition it boots from. The boot files or the file system on that volume are damaged, the boot configuration points at the wrong place, or the drive itself is failing, so Windows stops with a blue screen instead of starting with missing system files.
Will I lose my files if I run CHKDSK or bootrec?
Usually not. Startup Repair, CHKDSK, SFC, and the bootrec commands repair the file system and boot records without touching your personal files. Data loss becomes a real risk only if you format the drive during a reinstall, or if the drive is physically failing, so back up first whenever you can still read the drive from another PC.
Why did this happen after a Windows update or power cut?
An update or a sudden power cut can interrupt a write to the boot files or the file system, leaving them half-finished and inconsistent. Windows then cannot mount the volume on the next start. Removing the latest update from recovery, or running CHKDSK /r from Command Prompt, repairs that inconsistency in most cases.
Do I need a Windows installation USB to fix it?
Not always. After a few failed starts, Windows usually opens Automatic Repair by itself, and you can reach Command Prompt and Uninstall Updates from there. You need installation media only if Automatic Repair never appears, or if you must rebuild boot files that the on-board recovery tools cannot reach.