EaseUS Partition Master

Fix 'An Operating System Wasn't Found' Error When Booting

When you boot Windows, you may receive the error: An operating system wasn't found. This guideline will offer detailed instructions to help users fix this.

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Updated on May 27, 2024

Many Windows 10 users reported encountering a black screen issue with the error message "An operating System wasn't found. Try disconnecting any drives that don't contain an operating system. Press ctrl+alt+del to restart" after Windows update, BIOS update, or disk cloning. Don't panic! EaseUS will walk you through multiple solutions and provide a comprehensive tutorial to help you fix this error.

How to Fix An Operating System Wasn't Found Error

Follow the efficient methods below to resolve the An operating system wasn't found error when booting Windows:

Way 1. Perform a Windows Startup Repair

Option 1. Fast & Safe Boot Repair Tool

EaseUS Partition Master Professional can create bootable media to fix various boot issues, including an operating system not found and no boot device found. Compared to the Windows built-in startup repair tool, this effective software is more user-friendly and easy to use.

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Prepare a USB and refer to the easy steps:

Step 1. Start EaseUS Partition Master after connecting the external drive/USB to your computer, go to "Bootable Media," and click "Create bootable media."

create easeus partition master bootable disk

Step 2. Select an available USB Drive or CD/DVD and click "Create." You can also burn the Windows ISO file to the storage media.

create easeus partition master bootable disk

Step 3. Connect the created bootable drive to the new computer and reboot the computer by pressing and holding F2/Del to enter the BIOS. Then, set the WinPE bootable drive as the boot disk and press F10 to exit.

Step 4. Boot the computer again and enter the WinPE interface. Then, open EaseUS Partition Master and click "Boot Repair" under the "Toolkit" option.

open boot repair

Step 5: Select the system you want to repair and click "Repair."

click  repair

Step 6. Wait a moment, and you will receive an alert that the system has been successfully repaired. Click "OK" to complete the boot repair process.

click ok to complete the repair

This tool can solve more operating system/image corrupted or missing issues:

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Option 2. Windows Built-in Tool

Windows Startup Repair can automatically detect and repair startup problems on your PC. To use this tool, you need to create a bootable USB from ISO Windows 10 as an installation USB/CD:

Step 1. Connect the Windows boot media and set your computer to boot from it.

Step 2. Press any key when entering the "Press any key to boot from CD or DVD" window.

Step 3. In the Windows setup interface, select a language, time, and currency format. Then, click "Next."


Step 4. In the next screen, choose "Repair Your Computer."


Step 5. Choose "Troubleshoot" > "Advanced options" > "Startup Repair."


Way 2. Configure and Repair the Boot Files

Another way to fix "an operating system wasn't found" in Windows 10 is to configure and repair the boot files.

Note: To open the Command Prompt, you'll need a bootable USB or DVD that contains Windows 7 or above. Or, you can visit the official site and create a Windows bootable USB flash drive.

Step 1. Launch the Command Prompt:

  • Boot from Windows bootable media(DVD or USB).
  • In the Windows Setup screen, set up the Language, Time, and Keyboard settings
  • Press the SHIFT + F10 keys to launch the Command Prompt.

Step 2. Determine if your disk is GPT or MBR:

  • Type the following commands into the Command Prompt window, hitting Enter after each command:
  1. diskpart
  2. list disk
  • Check to determine if your disk has an asterisk (*) in the GPT column; if so, it is GPT. If not, the drive is configured as MBR.
  • Enter "exit" and hit Enter.

If your disk is MBR:

Step 1. Hit Enter after typing dir a:

  • If drive A: is detected and a directory appears, look inside the directory for the \Windows folder. The system drive is that if it is present. Go straight to step 2.
  • Type dir b: and hit Enter if the drive cannot be located or if the \Windows folder is not present on it. Go through the alphabet again until you find the drive containing the \Windows folder; do not search for the X: drive.

Step 2. Type :bcdboot C: when it has been located.\Windows/S C:

  • In this instance, the Windows folder was located on disk C. If the Windows folder is located on another drive, Replace "C" with the drive letter of that drive.

Step 3. Input diskpart and hit Enter. Then, type the following lines by pressing Enter for each:

  • list disk
  • select disk C
  • list volume
  • select volume C
  • active (You may receive a message that the volume has been successfully set as active)
  • exit

If your disk is GPT:

Step 1. Enter dir a: and hit Enter.

  • Look for the \Windows folder in the directory if drive A: is detected and a directory appears. That is the System Drive if it is present. Go directly to step 2.
  • Type dir b: and hit Enter if the drive cannot be located or does not have the \Windows folder on it. Skip the X: drive and keep going through the alphabet until you find the disk containing the \Windows folder.

Step 2. Type diskpart and press Enter. Then, type the command lines below and hit Enter after each in the diskpart window:

  • list disk
  • select disk C (Replace C with your system disk)
  • list part

Step 3. Locate the partition labeled as System. Assign the partition the letter R. You are free to select any unassigned letter in case the letter R is already taken. Enter the following commands and hit Enter after each to allocate the letter:

  • assign letter=r:
  • exit

Step 4. Then, enter the following commands in Command Prompt and press Enter after each line:

  • cd /d r:\EFI\Microsoft\Boot\
  • ren BCD BCD.bak
  • bcdboot c:\Windows /l en-us /s m: /f UEFI

Step 5. Reboot your computer from the command prompt using the quick command and hit Enter:

  • shutdown -f -r -t 00

Now, share these solutions to help Windows users repair the "An operating system wasn't found" error:


Way 3. Rebuild MBR via EaseUS Partition Master

 Rebuild the Master Boot Record will help users solve various boot problems. Rebuilding MBR using CMD is quite complicated and time-consuming. Don't worry. EaseUS Partition Master Free will get you covered with its powerful and free rebuild MBR feature:

Free Download 

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Step 1. Create a WinPE bootable disk

  • Launch EaseUS Partition Master, and click "Bootable Media" on the toolbar. Select "Create bootable media".
  • Click "Next" to finish the process.
create a bootable disk

Step 2. Boot EaseUS Partition Master Bootable USB

  • Connect the bootable USB or CD/DVD to your PC. 
  • Press F2 or Del when you restart the computer to enter the BIOS screen. Set and boot your computer from "Removable Devices" or "CD-ROM Drive". And then EaseUS Partition Master will run automatically.

Step 3. Rebuild MBR

  • Click "Toolkit" and choose "Rebuild MBR".

rebuild MBR

  • Select the disk and the type of MBR. Then, click "Rebuild".
rebuild MBR
  • After that, you can see "MBR has been successfully rebuilt on Disk X".
rebuild MBR

You can learn additional information from the related article:

related articles

[Full Guide] How to Rebuild MBR | Fix Damaged MBR

In this post, you will discover a step-by-step tutorial of how to rebuild MBR on a Windows computer.


Way 4. Reinstall the Windows

If the above fixes can't solve this error, you can reinstall the Windows from the official site.


In conclusion, the "An Operating System Wasn't Found" message can be annoying when booting your Windows 10 PC. Luckily, adhering to the instructions provided in this article, you should be able to fix the problem and quickly restore your system's functionality. To avoid future occurrences of such mistakes, remember to periodically back up your vital files and let EaseUS Partition Master help you get out of unbootable black screen issues seamlessly.

Free Download 

Windows 11/10/8/7100% Secure

FAQs About An Operating System Wasn't Found

If you still have some queries about the "An Operating System Wasn't Found" error in Windows, follow us in this FAQ section:

1. Why was an operating system not found?

There are some possible causes, including a damaged disk, a corrupt boot record, a BIOS that failed to recognize the hard drive, a missing or corrupt command.com file, or a virus infection.

2. How do I recover my lost operating system?

You can download the operating system files from the official website or use an installation media (CD, DVD, or USB).

3. How do I fix the boot device not found?

Here are some solutions that you can take:

  • Check Your BIOS settings and boot order. ...
  • Hard reset the computer
  • Check the bad sectors
  • Fix corrupted MBR

Further Information: How to Fix a No Bootable Devices Found Error

How Can We Help You

About the Author

Updated by Roxanne

Roxanne is one of the main contributors to EaseUS and has created over 200 posts that help users solve multiple issues and failures on digital devices like PCs, Mobile phones, tablets, and Macs. She loves to share ideas with people of the same interests.

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