What Does the INACCESSIBLE_BOOT_DEVICE Error Mean on Windows
Its specific causes (AHCI/RAID mode, a moved disk) and how to fix it without reinstalling.
A blue screen with the message "INACCESSIBLE_BOOT_DEVICE" — essentially, Windows has lost communication with the disk it's installed on, right at the moment of starting up.
The specific causes of this particular error
- You changed the storage mode in the BIOS/UEFI (from AHCI to RAID, or vice versa) without noticing. Windows stays configured for one mode and the BIOS presents it with another — they don't recognise each other. This is the most specific cause of this error, and the easiest to fix if it's your case.
- You moved the disk to another computer, or changed motherboards. The installed storage driver doesn't match the new hardware.
- A Windows update installed an incompatible storage driver.
- The file system is damaged, from an abrupt shutdown or a failure of the disk itself.
First: check the AHCI/RAID mode in the BIOS
If you recently touched the BIOS (even by accident), go back in and check the storage configuration section (SATA). If it was on AHCI, confirm it's still on AHCI, not RAID (or vice versa) — reverting this specific change resolves the error immediately in these cases, with nothing else needed.
For the other causes
Follow the same general steps as any boot failure: enter the
recovery screen and try, in this order, Startup Repair → Uninstall the
latest update → System Restore → the bootrec commands. We
cover this in more detail in our guide on
the computer won't start: diagnosis guide.
Checking the disk in case the problem is physical
From Command Prompt in the recovery menu:
chkdsk C: /f /r
Note: with the /r parameter, this
command can take quite a while (even several hours on large disks)
because besides fixing errors, it looks for physically damaged
sectors. Don't interrupt it once it's started.
Warning: if after trying all of the above the error persists and you suspect the disk might be physically failing, prioritise recovering your important files before continuing to attempt further repairs.
Frequently asked questions
Is it always necessary to reinstall Windows after this error?
No, in most cases it can be resolved without reinstalling — by reverting an AHCI/RAID mode change in the BIOS, uninstalling a problematic update, or repairing the boot record with the bootrec commands.
Why does it show up right after changing motherboards?
Because the storage driver Windows had loaded corresponds to the previous hardware, and it doesn't recognise the new one. It's a common and expected cause when moving a disk between different machines.
Can CHKDSK with /r make things worse if the disk is already failing?
It usually doesn't make the problem worse, but it is slower and more demanding on the disk than a basic check. If you already suspect a serious physical failure, prioritise recovering your files before running it.