Windows not booting after converting from mbr to gpt

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  1. Posts : 59
    windows 10
    Thread Starter
       #21

    The mobo supports uefi and from what I read it automatically switch to uefi when csm is disabled
      My Computer


  2. Posts : 4,594
    Windows 10 Pro
       #22

    Well on my board I have it Enabled and it gives me 3 choices, UEFI & Legacy Boot, Legacy, or UEFI

    I leave it at the 1st option.

    If I disable it, it doesn`t list any Boot options.
      My Computers


  3. Posts : 4,511
    several
       #23

    You are going to have to fix it from another os or boot media.

    What have you got in that department?
      My Computer


  4. Posts : 7,606
    Windows 10 Home 20H2
       #24

    TheViper said:
    Does a uefi clean install delete all partitions or just C?
    Years ago, I used Linux Mint to convert the system disk from MBR to GPT without data loss and then clean installed Windows 10 in UEFI mode after deleting only Windows partitions without touching the data partition, drive D.

    TheViper said:
    Asrock h81m
    I have been using H81M too.

    TheViper said:
    The mobo supports uefi and from what I read it automatically switch to uefi when csm is disabled
    My CSM is enabled although I use UEFI.
      My Computer


  5. Posts : 4,594
    Windows 10 Pro
       #25

    Ya I think it has to be Enabled or there`s no list of boot choices, I just tried it.

    Just leave it at UEFI & Legacy OPROM and you`ll never need to change it.

    The only change you`ll have to make is OS Type, from Other OS, to Windows UEFI Mode, under Secure Boot which has to be Enabled.

    Oh and here is something I remember from using the MBR2GPT /convert /allowFullOS command on the X299

    I had to use my Macrium Rescue USB stick to repair the Boot record.
    Last edited by AddRAM; 06 Oct 2021 at 02:17.
      My Computers


  6. Posts : 7,606
    Windows 10 Home 20H2
       #26

    I have never changed the following default settings:

    Windows not booting after converting from mbr to gpt-other-os.jpg

    Windows not booting after converting from mbr to gpt-uefi-legacy.jpg
      My Computer


  7. Posts : 18,424
    Windows 11 Pro
       #27

    @TheViper,

    If you have a Windows 10 installation USB flash drive you can boot the computer from, at the first screen press Shift + F10 to open a command prompt. Or use any other way to get to a command prompt, such as booting from a Macrium Reflect or other rescue type USB flash drive.

    I am assuming you have a single drive in the computer. Run:

    Code:
    diskpart
    list disk
    select disk 0  <-0 should be your main drive, if it isn't, change the number to match your main drive
    list part
    Do you see a small system partition listed, like my 100 mb System partition?

    Code:
    Microsoft Windows [Version 10.0.22000.194]
    (c) Microsoft Corporation. All rights reserved.
    
    C:\WINDOWS\system32>diskpart
    
    Microsoft DiskPart version 10.0.22000.1
    
    Copyright (C) Microsoft Corporation.
    On computer: JOHN-LAPTOP
    
    DISKPART> list disk
    
      Disk ###  Status         Size     Free     Dyn  Gpt
      --------  -------------  -------  -------  ---  ---
      Disk 0    Online          476 GB   588 MB        *
      Disk 1    Online          476 GB  2048 KB        *
    
    DISKPART> select disk 0
    
    Disk 0 is now the selected disk.
    
    DISKPART> list part
    
      Partition ###  Type              Size     Offset
      -------------  ----------------  -------  -------
      Partition 1    System             100 MB  1024 KB
      Partition 2    Reserved            16 MB   101 MB
      Partition 3    Primary            347 GB   117 MB
      Partition 4    Primary            128 GB   348 GB
    
    DISKPART>
      My Computer


  8. Posts : 6,247
    Windows 11 Pro - Windows 7 HP - Lubuntu
       #28

    You have converted your drive from MBR to GPT but it didn't created the EFI - Fat32 100M partition that has the boot manager to boot as UEFI-GPT.
    You don't need to reinstall Windows
    You must create a EFI - Fat32 100M partition and load a boot manager on it.
    The MBR System partition can be converted to EFI - Fat32 100M partition.
    Follow NavyLCDR instructions and you will have your computer booting as UEFI-GPT
      My Computers


  9. Posts : 59
    windows 10
    Thread Starter
       #29

    Thanks for all the answers, I will have the USB ready tomorrow because I don't have a pc to burn the iso so I will use a friend's pc to burn it
    @Megahertz
    How do I create the EFI partition? NavyLCDR instructions only shows how to check if I have the partition or not how to create it and load boot manager on it
      My Computer


  10. Posts : 6,247
    Windows 11 Pro - Windows 7 HP - Lubuntu
       #30

    TheViper said:
    Thanks for all the answers, I will have the USB ready tomorrow because I don't have a pc to burn the iso so I will use a friend's pc to burn it
    @Megahertz
    How do I create the EFI partition? NavyLCDR instructions only shows how to check if I have the partition or not how to create it and load boot manager on it
    The first step is to find out your drive layout

    Boot from a a Windows 10 installation USB flash drive and at the first screen press Shift + F10 to open a command prompt. Type the code below:
    Code:
    diskpart
    list disk (take note of your drive number n)
    select disk n  (change n with the drive number you found above)
    list part (It will list all the drive partitions. Take note of your System partition number x and Windows partition number z)
    Once you find out the the drive number, the System partition number and Windows partition number then we can give you the instructions to format it to Fat32 and to load it with the boot manager.
    Last edited by Megahertz; 06 Oct 2021 at 15:59.
      My Computers


 

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