How to fix 'An operating system not found' error on Windows 10 and Windows 8.1

The " An operating system not found" error is a common one that usually happens on Windows 10 or Windows 8.1. This error occurs after the user upgrades Windows (from Windows 8.1 to Windows 10), updates the BIOS, . If the screen of your Windows 10 or Windows 8.1 computer displays a message "An operating system wasn Try finding disconnected any drives that do not contain the operating system. Press Ctrl + Alt + Del to restart " , follow the steps below to fix the error.

1. Use Windows' Startup Repair tool

1. Insert Windows Boot Media into your computer and start the computer from there.

2. On the first setup screen, select Language, time and currency format and Keyboard input, then click Next.

3. On the next window, select Repair your computer.

4. Next click on Troubleshoot => Advanced options => Startup Repair.

5. Wait for Windows to find and fix the error.

6. After the Startup Repair is complete, proceed to restart your Windows computer.

2. Configure and repair boot files (boot files)

1. Insert Windows Boot Media into your computer and start the computer from there.

2. On the first setup screen, select Language, time and currency format and Keyboard input, then click Next.

3. In the next window, press Shift + F10 key combination to open the Command Prompt window.

4. On the Command Prompt window, enter the following command and press Enter to open the DISKPART utility:

diskpart

5. Enter the following command into Command Prompt and press Enter to check if your drive is set to GPT or MBR partition:

list disk

At GPT column, you find:

- If you see the sign icon (*), it means that the Partition Table of the drive is GPT.

- If you don't see the sign icon (*), the drive's Partition Table is MBR.

6. Enter Exit in the Command Prompt window and press Enter.

7. If the partition is MRB, follow the steps below:

Part 1: Fix boot file error (boot file) on MBR partition:

1. First find the Windows installation drive. To do this, on the Command Prompt window, enter the following command into:

dir C:

Note:

If the Windows folder is displayed, follow the steps below. If the Windows folder is not displayed, enter the commands by replacing C: with the names of other drive letters (such as dir d :, dir e :, .) until the mail folder is found. Windows entry.

2. After finding the drive with the Windows folder, enter the following command to create the boot files (boot files) on the drive and press Enter:

bcdboot D: Windows / SD:

Note:

If Windows is stored on another drive, replace D with the Windows drive letter.

3. After the Boot file is created, open the DISKPART prognosis again by entering the following command into the Command Promt window:

diskpart

4. At DISPART, enter:

list disk

5. Enter the command below into the Command Prompt window and press Enter:

select disk X

Note:

In the statement above X is the number of drives containing the operating system, such as drive 0.

6. Enter each statement below into the Command Prompt window and press Enter:

1. list volume

2. select volume X (where X is the Volume number containing the Windows folder. In the example above the volume is 3).

3. active

7. Enter exit to close the DISPART tool.

8. Close all windows and restart your computer.

9. Now you can remove Windows 10 Boot Media and restart your computer normally.

Part 2: Fix boot file errors (boot files) on GPT partitions

1. First find the Windows installation drive. To do this, on the Command Prompt window, enter the command below and press Enter:

dir C:

Note:

If the Windows folder is displayed, follow the steps below. If the Windows folder is not displayed, enter the commands by replacing C: with the names of other drive letters (such as dir d :, dir e :, .) until the mail folder is found. Windows entry.

2. Next open the DISKPART utility by entering the command below into the Command Prompt window and then press Enter:

diskpart

3. At the DISKPART command, you enter:

list disk

4. Next enter the following command and press Enter:

select disk X

Note : in sentence l, above command, X is the number of drives containing the operating system

5. Enter the command below and press Enter:

list partition

6. Find the partition named System .

7. Select the System partition by entering the command:

select phân vùng X

Note : where X is the partition number named System

8. Assign a drive to the System partition by entering the following command into the Command Prompt window and press Enter:

assign letter = S:

Note:

In the above statement, replace S with the drive letter name.

9. Enter exit into the Command Prompt window and press Enter to close the DISKPART tool.

10. Enter each statement below, after each statement press Enter:

1. cd / d S: EFIMicrosoftBoot

2. ren BCD BCD.bak

3. bcdboot C: Windows / l en-us / sm: / f UEFI

Note:

1. Replace S with the drive name you assigned to the System partition.

2. If Windows is on another drive, use that drive name to replace C.

3. In the third statement, the "/ l en-us" section used to set up the Windows language is English. If you want to set up another language, replace "/ l en-us" with the appropriate language code.

11. Close all windows and restart your computer.

12. You can now remove Windows 10 Boot Media and restart your computer normally.

Refer to some of the following articles:

1. 4 ways to fix USB errors without formatting: 'Windows was unable to complete the format'

1. Summary of some ways to fix Windows 10 crash, BSOD error and restart error

1. Unusually high CPU error correction due to TiWorker.exe on Windows 10 / 8.1 / 8

Good luck!