How to Fix “An Operating System Wasn’t Found” Boot Error in Windows

When starting your computer, you may see this black-screen error:

This error means the computer cannot find a valid Windows boot loader or a bootable operating system on the selected disk. In many cases, Windows is still on the hard disk or SSD, but the computer cannot start it because of an incorrect BIOS/UEFI setting, wrong boot order, damaged boot files, corrupted BCD configuration, or boot sector problems.

Step 1: Check BIOS/UEFI First

Before using any boot repair tool or command-line repair method, restart the computer and enter the BIOS/UEFI setup screen. Common BIOS/UEFI keys include F2, Del, Esc, F10, and F12. Press the key immediately after powering on the computer.

Step 2: If the Disk Is Detected but Windows Still Cannot Boot

If the hard disk or SSD is detected in BIOS/UEFI and the boot order looks correct, the Windows boot files or boot configuration may be damaged.

• Damaged MBR
• Damaged boot sector
• Incorrect boot indicator
• Corrupted BCD file
• Missing Windows boot files
• File system errors on the boot partition
• Boot configuration damaged after disk clone, restore, repartitioning, or system crash
• Wrong UEFI/Legacy boot mode after hardware or BIOS setting changes

Method 1: Repair the Boot Error Using Windows Commands

This method uses Windows Recovery Environment or a Windows installation USB disk. It is suitable for advanced users who are comfortable identifying partitions and running command-line tools.

Step 1: Boot into Command Prompt

Boot the computer from a Windows installation USB disk. On the Windows Setup screen, click:

Repair your computer → Troubleshoot → Advanced options → Command Prompt

Do not click Install now.

Step 2: Find the Windows Partition

Drive letters in Windows Recovery Environment may be different from normal Windows. Run:

diskpart
list volume

Look for the Windows partition. It is usually a large NTFS partition. Exit DiskPart:

exit

Then test possible drive letters:

dir C:\Windows
dir D:\Windows
dir E:\Windows

Use the drive letter that contains the Windows folder. In the examples below, we assume the Windows partition is C:. If your Windows partition is D:, replace C:\Windows with D:\Windows.

Repair Method A: For UEFI/GPT Systems

UEFI / GPT

Use this method if Windows was installed in UEFI mode and the disk uses GPT. Most modern Windows 10 and Windows 11 computers use UEFI/GPT.

Find the small FAT32 EFI System Partition, usually around 100 MB to 300 MB:

diskpart
list volume

Assign the EFI System Partition a drive letter:

select volume X
assign letter=S:
exit

Replace X with the correct EFI partition volume number. Then rebuild the EFI boot files:

bcdboot C:\Windows /s S: /f UEFI

If the command succeeds, you should see:

Boot files successfully created.

Restart the computer:

wpeutil reboot

Repair Method B: For Legacy BIOS / MBR Systems

Legacy / MBR

Use this method if Windows was installed in Legacy/CSM mode and the disk uses MBR.

bootrec /fixmbr
bootrec /fixboot
bootrec /scanos
bootrec /rebuildbcd

If bootrec /fixboot shows Access is denied, you can continue by rebuilding the boot files with bcdboot.

If there is a System Reserved partition

diskpart
list disk
select disk 0
list partition

Find the small System Reserved partition. It is usually NTFS and around 100 MB to 600 MB. Select it and mark it active:

select partition X
active
assign letter=S:
exit

Replace X with the correct System Reserved partition number. Then rebuild boot files:

bcdboot C:\Windows /s S: /f BIOS

wpeutil reboot

If there is no System Reserved partition

If Windows is installed directly on the active system partition, mark the Windows partition active and rebuild boot files:

diskpart
list disk
select disk 0
list partition
select partition X
active
exit

Replace X with the Windows partition number. Then run:

bcdboot C:\Windows /s C: /f BIOS

wpeutil reboot

Optional: Check the File System

If the boot partition has file system errors, run:

chkdsk C: /f

If your Windows partition uses a different drive letter in Windows Recovery Environment, replace C: with the correct letter.

chkdsk D: /f

Method 2: Repair the Boot Error with Lazesoft One Click Fix

If you do not want to manually identify partitions and type commands, use Lazesoft Recovery Suite Home Edition or Lazesoft Windows Recovery Home Edition. The One Click Fix feature can automatically check and repair common Windows boot problems.

Step 1: Boot from a Lazesoft Recovery USB Disk

Boot the problem computer from a Lazesoft recovery USB disk. After Lazesoft Recovery Suite starts, select Windows Recovery from the main screen.

Step 2: Choose One Click Fix Crash Solution

In Lazesoft Windows Recovery, choose One Click Fix Crash Solution. This option is designed for common Windows boot and crash problems.

Then click the One Click Fix button.

Step 3: Select the Windows Installation

If Lazesoft finds more than one Windows installation, select the correct Windows installation you want to repair. Check the Windows version, boot volume, disk size, and system volume information carefully before continuing.

Step 4: Run One Click Fix

Lazesoft One Click Fix will check and repair common Windows boot problems automatically. It may check and fix the MBR, boot indicator, boot sector parameters, boot sector boot code, BCD file, file system on the boot partition, missing critical Windows system files, and Windows boot-related registry files.

Step 5: Reboot and Test Windows

After the repair is completed, click Finish, remove the Lazesoft USB disk, and restart the computer.

If the boot repair is successful, Windows should start normally again. In some cases, you may see a Windows Boot Manager screen first. Select the correct Windows entry and press Enter.

What If the Error Still Appears?

1. Confirm the Windows disk is still listed in BIOS/UEFI.
2. Check whether the correct disk is first in the boot order.
3. Confirm the correct boot mode: UEFI or Legacy/CSM.
4. Disconnect extra USB drives, external disks, and memory cards.
5. Check whether the Windows disk has hardware problems.
6. If the computer uses RAID, Intel RST, Intel VMD, or a special storage controller, make sure the correct storage driver is available in the recovery environment.
7. If Windows was cloned or restored to a new disk, check whether the target disk uses the expected partition style: GPT for UEFI or MBR for Legacy boot.

Which Method Should You Use?

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