What the error means (plain English)
“A required device isn’t connected or can’t be accessed”
Windows is saying:
- The disk is there, but
- The boot files (EFI/BCD) are missing, damaged, or pointing to the wrong place
Common causes:
- Dual-boot install (Linux / another Windows)
- Disk mode change (AHCI ↔ RAID)
- Failed Windows update
- Cloned disk / replaced SSD
- Corrupt EFI partition
First: try the quick options on that screen
Press F9 – Use a different operating system
- If Windows appears → select it
- If it boots → problem is just default boot order
Press F8 – Startup Settings
- Try Startup Repair
- If it fails → continue below
Proper fix (recommended): Repair the boot files
You’ll need a Windows 10/11 USB installer.
Step 1: Boot into Windows Recovery
-
Insert Windows USB
-
Power on → press F12 / F9 / Esc (depends on PC)
-
Boot from USB
-
Choose Repair your computer
-
Go to:
Troubleshoot → Advanced options → Command Prompt
Step 2: Identify the EFI partition
In Command Prompt, type:
diskpart
list disk
select disk 0
list vol
Look for:
- FAT32
- Size ~100–300 MB
- Label like EFI or System
Example:
Volume 1 FAT32 100 MB
Select it:
select vol 1
assign letter=S
exit
Step 3: Rebuild Windows boot files (MOST IMPORTANT)
Now run:
bcdboot C:\Windows /s S: /f UEFI
If Windows is on another drive (like D:), adjust accordingly.
You should see:
Boot files successfully created
Step 4: Restart
exit
Remove the USB and reboot.
In most cases, Windows will boot normally.
If it still fails
Try these extra commands (same Command Prompt):
bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd
If /fixboot says Access denied, the bcdboot method above is still the correct fix.
BIOS/UEFI checks (very important)
Enter BIOS setup and confirm:
-
Boot Mode: UEFI
-
Secure Boot: Enabled (or temporarily disabled if testing)
-
SATA Mode:
- If Windows was installed on AHCI, keep AHCI
- RAID ↔ AHCI changes can trigger this error
Why this happens a lot on Dell / HP / Lenovo
- Windows Update touches boot files
- Dual-boot overwrites EFI
- BIOS update resets boot order
Summary (quick fix checklist)
Disk is detected
EFI partition exists
BCD rebuilt using bcdboot
BIOS set to UEFI + correct disk mode