Boot error INACCESSIBLE_BOOT_DEVICE is caused either by missing driver for bootable storage device, or by wrong state of HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices registry key.
Learn how to fix INACCESSIBLE_BOOT_DEVICE by updating reference to disk C: in SYSTEM registry hive using Emergency Boot Kit.
1. Symptoms of this problem
When Windows 10 or Windows 11 is loading, an error message like this appears:
Your PC ran into a problem and needs to restart.
*** STOP: 0x0000007B
2. Cause of this problem and scope of this article
This error may occur in multiple contexts and due to multiple reasons:
The rest of this article assumes case (5) only. For other cases please refer to other articles listed above or to the official Microsoft documentation on Bug Check 0x7B: INACCESSIBLE_BOOT_DEVICE.
3. Synopsis of INACCESSIBLE_BOOT_DEVICE error
Windows maintains a database of mapping between drive letters (such as C:, D:, E:) and volume identifiers (containing disk signature + partition offset for volume on MBR disk, or GUID for volume on GPT disk). It is stored in HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices registry key.
This mapping can become obsolete or invalid if/when partition corresponding to disk C: is moved on disk, if/when neighbour partitions on the same disk are resized or moved, due to interrupted registry transaction, due to power loss during Windows update, due to failed disk block allocated to the \Windows\System32\Config\SYSTEM registry hive and other similar reasons.
The essence of INACCESSIBLE_BOOT_DEVICE error is that Windows is no longer able to figure out where is its disk C:
If driver for underlying storage device is present in Windows OS, then INACCESSIBLE_BOOT_DEVICE error can be trivially fixed by updating reference to disk C: in the HKEY_LOCAL_MACHINE\SYSTEM\MountedDevices registry key.
4. How to fix INACCESSIBLE_BOOT_DEVICE (step by step guide)
1) Download Emergency Boot Kit and deploy it to USB thumbdrive according to the instructions, then set up your BIOS to boot from USB thumbdrive. You need full version of Emergency Boot Kit to actually write changes to the disk, but it's recommended to try demo version to make sure there are no hardware incompatibilities.
2) Boot the Emergency Boot Kit:
3) Choose Mount & Boot Center in the main menu, wait while it loads:
4) Make sure Mount & Boot Center looks like below (partition with Windows OS which should be mounted as "C:" isn't actually mounted as "C:"):
5) Set proper mount path for system partition. It's always "C:" for Windows 11/10/8.x/7/Vista, and it's usually "C:" but may be different for Windows XP. If unsure, run Emergency Boot Kit Registry Editor and check HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Setup\BootDir:REG_SZ.
6) Click OK to close Mount & Boot Center (changes will be commited to disk at this point), then choose "Reboot" in main menu of Emergency Boot Kit: