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Error Operating system not found in Windows 10

Yesterday, I upgraded my computer from Windows 8 to Windows 10. The upgrade was very successful, but after that, I could not start my computer. It says "Cannot find the operating system. Try to disconnect any drive that does not contain the operating system. Press Ctrl + Alt + Del to restart."

Error: "Operating system not found" in Windows 10
The following error "Operating system not found." Try to disconnect any drive that does not contain the operating system. During the operating system startup process, "Press Ctrl + Alt + Del to restart" may appear in Windows 10. This error may be displayed after upgrading Windows, such as from Windows 8 to Windows 10, updating the BIOS, or cloning one hard drive to another. No matter what triggers this error, here are some useful ways to solve the "Cannot find the operating system in Windows 10" issue.
How to solve the "OS not found" problem in Windows 10?
To fix the "Windows 10 operating system not found" issue, you must have a USB installation device. If you don't have one, you can use MediaCreationTool to create installation media.

Before making the following fixes, you can try first:
1. Configure your internal hard drive as the operating system of the first boot device installed in the BIOS settings.
2. Disconnect any other devices that do not contain your operating system, such as a mouse, keyboard, etc.

Method 1. Perform Windows startup repair
Windows startup repair can fix many problems related to Windows startup failure. So you can try this method first.
1. Connect the Windows USB installation media to the PC and boot from it.
2. In the first setting window, select the language, time and currency format, and Keyboard or input method. When finished, click "Next" to continue.
3. In the second window, click "Repair your computer".
4. Then click "Troubleshooting"> "Advanced Options"> "Startup Repair".
Wait a few seconds before it completes. After startup repair is complete, try to start Windows again.

Method two. Configure and repair the startup file
If the above method does not help to fix the "OS not found" in Windows 10, you can consider configuring and repairing the startup file.
1. Connect the Windows USB installation media to your PC and boot from it.
2. In the first setting window, select the language, time and currency format, keyboard or input method to be installed, and then press "Next" in Method 1.
3. In the second window, press "SHIFT + F10" to bring up the command prompt.
4. In the command prompt window, type "diskpart" and press "ENTER" to open the DiskPart interface.
5. Then enter "list disk" to see if your disk is in GPT or MBR, and then press "ENTER".
6. Find the GPT column and check if it contains an asterisk "*".
-If you see an asterisk, it means your disk is on GPT.
-If you don’t see an asterisk, it means your disk is in MBR.
7. Type "exit" and press "ENTER".

If the partition is in MBR, go to Part 1 to find a solution; if the partition is in GPT, please read Part 2 to solve the problem.

Part 1. For MBR system driver
First, you need to find out which hard drive the system is installed on.
1. At the command prompt, type "dir c:" and press "ENTER". If the Windows folder is displayed, continue to the next step; otherwise, continue typing the next letter in the alphabet until you find which partition has a Windows folder (for example, dir d:, dir: e, dir: f...). (In this example, drive D contains the Windows folder.)
2. Type "bcdboot D:\Windows/SD:" at the command prompt, and you should see the message "Start The file has been successfully created".
3. After creating the boot file, reopen the DiskPart window by typing "diskpart".
4. In DiskPart, type "list disk".
5. Type "select disk x". "X" stands for the disk number containing the operating system, for example. For example, "0".
6. Enter "list volume" and press "ENTER".
7. Enter "Select Volume x". "X" represents the partition number containing the Windows folder. In this example, it is "3".
8. Enter "active" and press "ENTER".
9. Type "exit" and press "ENTER" to exit DiskPart.
10. Close all windows and restart the PC.
11. Remove the Windows 10 boot device and boot Windows 10 as usual.

Part 2. For GPT system drive
1. Use the method mentioned at the beginning of Part 1 to find the disk where Windows is located.
2. Type "diskpart" and press "ENTER" to open the DiskPart utility.
3. At the DiskPart prompt, type "list disk" and press "ENTER".
4. Now, type "select disk x" and press "ENTER". "X" means the disk number containing the operating system, for example. For example, "0").
5. Enter "partition list" and press "ENTER".
6. Check which partition is marked as "system". In this example, it is partition 4.
7. Enter "select partition x" to select the system partition. "X" stands for the partition number marked "System". For example, "4".
8. Type "assign letter = S:" and press the "ENTER" key to assign a drive letter (for example, "s") to the system partition.
9. Type "exit" and press "ENTER" to exit the DiskPart window.
10. Next, enter "cd / d S:\EFI\Microsoft\Boot\" and press "ENTER".
11. Type "ren BCD BCD.bak" and press "ENTER".
12. Enter "bcdboot C:\Windows/l en-us/s S:/f UEFI" and press "ENTER".
13. Close all windows and restart the PC.
14. Remove the Windows 10 boot device and boot Windows as usual.

Method 3. Rebuild MBR with free third-party software
Yes, I think Method 2 is too complicated, we are still Looking for alternative ways to fix Windows 10 "OS not found" error, maybe it's time to try some third-party software. Using the powerful and simple disk management software AOMEI Partition Assistant Standard Edition, you can rebuild the MBR to fix this Windows startup error once and for all. In addition to this useful feature, you can also try its other features to repair damaged SSD, black screen startup errors, or convert between GPT and MBR.
Step 1. After entering the main interface of AOMEI Partition Assistant Standard Edition, select the system hard disk, right-click and select "Rebuild MBR".
Step 2. Set the MBR type of the current operating system and press "OK"
Step 3. After returning to the main interface, click "Apply" in the upper left corner and press "Continue" to Start MBR reconstruction.
You should wait a few seconds before it completes.















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