Windows · Windows Server · critical · Recovery, imaging & repair

"Operating system not found" or "No bootable device"

The firmware found no boot entry it can use — either the disk is not visible, or the boot files are gone.

What you see

A firmware message before Windows starts. Nothing on screen mentions Windows at all, which is the clue that this is earlier than a Windows fault.

What is actually wrong

The boot mode has changed between UEFI and legacy, the drive is not being detected, the boot order has changed, or the EFI system partition has been damaged or removed.

Codes and articles

Operating system not foundNo bootable device0xc00002250xc0000098Reboot and select proper boot device

Fixes (3)

Establish whether the disk is present

Firmware settings30 minuteslow riskreversible

The drive is not listed in the boot menu.

Enter the firmware setup and look at the storage configuration. If the drive is absent there, no software fix applies.
Check the SATA or NVMe mode has not changed — a switch from AHCI to RAID or Intel VMD hides the drive from a Windows install that was not built for it.
Reseat the drive and its cables. On a laptop, an M.2 drive working loose from thermal cycling is common and presents exactly like this.
Test the drive in another machine or a USB enclosure to separate a dead drive from a dead port.
If the drive is detected but reports zero capacity or an odd model name, it has failed. Recover the data professionally if it matters.

Confirm it workedThe drive is listed in the firmware with its correct model and size.

If you need to undo itNot applicable.

Match the boot mode to the disk layout

Firmware settings and WinRE40 minutesmedium riskreversible

The drive is visible but not bootable.

Boot Windows installation media and open a Command Prompt from Repair your computer.
Check the partition style. GPT needs UEFI mode; MBR needs legacy or CSM.
Command Prompt
```
diskpartlist diskrem the GPT column shows an asterisk for GPT disksexit
```
This mismatch is the single most common cause after a firmware update or a CMOS reset, which can silently revert the boot mode to the manufacturer default. Nothing is broken — the firmware is simply looking for the wrong kind of boot record.
Set the firmware to match: UEFI with CSM off for a GPT disk, legacy for MBR.
Check Secure Boot as well — it requires UEFI, and enabling it while the machine is in legacy mode leaves nothing bootable.
If the machine must run UEFI and the disk is MBR, convert it.
Command Prompt
```
mbr2gpt /validate /disk:0mbr2gpt /convert /disk:0
```

Confirm it workedThe Windows Boot Manager entry appears in the firmware boot order and the machine starts.

If you need to undo itThe firmware setting can be changed back. Image the disk before running mbr2gpt.

Rebuild the EFI system partition

WinRE Command Prompt45 minutesmedium riskreversible

UEFI mode is correct and the boot entry has still gone — commonly after a Linux install, a partition tool, or a clone.

Identify the Windows volume and the EFI partition. The EFI one is small, FAT32, and usually hidden.
Command Prompt
```
diskpartlist volume
```
Give the EFI partition a letter.
Command Prompt
```
sel vol 2assign letter=S:exit
```
Write a fresh boot store from the Windows installation.
Command Prompt
```
bcdboot D:\Windows /s S: /f UEFI /l en-gb
```
This is the whole repair in one command. It creates the EFI directory structure and the boot configuration from the installed Windows, which is far more reliable than trying to patch a damaged store.
If the EFI partition is missing entirely, create one of 100–500MB, format it FAT32, and then run bcdboot.
Command Prompt
```
diskpartsel disk 0create partition efi size=260format quick fs=fat32 label=SYSTEMassign letter=S:exit
```
Remove the drive letter and restart.
Command Prompt
```
diskpartsel vol 2remove letter=S:exit
```

Confirm it workedThe machine boots, and the boot store lists a single valid Windows entry.

Command Prompt

bcdedit /enum firmware

If you need to undo itTake an image of the disk before creating partitions. bcdboot itself only writes boot files.

Related faults

Where this stops. This write-up was written and checked by hand. It says what each step changes, how to confirm it worked and how to reverse it, and anything destructive is flagged before you reach it. If it does not match what your machine is doing, search the Support Centre for the exact code or message — and when something needs a person, get in touch.