[Solved!]The Selected Disk Is Not A Fixed MBR Disk on Windows 11/10

Convert GPT to MBR

If you have formatted the disk as GPT, you cannot mark the partition located on a GPT disk as active, because GPT-associated UEFI boot mode cannot recognize the concept of an active command. Thus, you need to convert GPT to MBR to fix the error message 'the selected disk is not a fixed MBR disk.'

The conversion from GPT to MBR automatically deletes all contents on the disk. Therefore, you should back up your disk in advance to avoid data loss. To guarantee the success of the conversion, you'd better run the command of cleaning disk to remove data from the disk. Let's dive into the details.

1. Click Win + R, and type cmd in the Run window.
2. Open Command Prompt as an administrator and type diskpart.
3. Type list disk and press Enter. 
4. Type select disk 1, replace the disk number with that of your GPT disk, and press Enter.
5. Type clean and press Enter to remove all the contents of the disk.
6. Type convert MBR and press Enter.
7. Type exit to quit Command Prompt.  
    

Conclusion

When you encounter the error message 'the selected disk is not a fixed MBR disk' in the diskpart utility, you can apply the solutions provided in this post to get rid of it. After that, you can continue to mark the target partition as active and boot your computer from it.

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