INACCESSIBLE_BOOT_DEVICE
Windows lost access to the drive it boots from. Common after a BIOS setting change (SATA mode), a failed update, or a dying drive.
How to fix it
- If you changed the SATA mode in the BIOS (AHCI, RAID or Intel RST/VMD), change it back. See the BIOS key page to get in.
- Let Windows fail to boot twice to reach Advanced startup, then try Startup Repair.
- If it started after an update: Advanced startup > Troubleshoot > Advanced options > Uninstall Updates.
- Check the drive is detected in the BIOS. If not, it may have failed.
Is it serious?
Often a setting. If the BIOS does not see the drive, it needs replacing.