How to Fix MBR2GPT Cannot Find OS Partition? [4 Solutions]

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Why MBR2GPT cannot find OS partition? According to a survey, the error can be caused by corrupted BCD data and inactive system partition on the hard disk. Don’t worry. Here we summarize some effective fixes to the error.

Solution 1. Convert MBR to GPT via MiniTool Partition Wizard

When it comes to converting MBR to GPT on Windows, most users may want to use MBR2GPT. But this tool has some limitations and always runs into various errors like “MBR2GPT cannot find OS partition for disk 0”.

Is there an alternative to MBR2GPT? Of course, yes! MiniTool Partition Wizard can help you convert MBR to GPT without data loss easily and vice versa. It is a professional partition manager that boasts many powerful features, such as extending partitions, changing cluster size, rebuilding MBR, migrating OS, etc.

Here’s how to convert MBR to GPT using the tool.

Step 1. Open the MiniTool software to enter its main interface, select your desired disk, and click on Convert MBR Disk to GPT Disk from the left action panel.

Step 2. Click on OK and then Apply to confirm this change.

Solution 2. Mark the System Partition as Active

Some users from the answers.microsoft.com forum reported that the “MBR2GPT failed to find OS partition” error can be solved by re-activating the system partition. However, the Mark Partition as Active” option is greyed out in Disk Management.

In this case, you can use the free partition software – MiniTool Partition Wizard to set a partition as active/inactive easily. Here you can set the system partition as active or mark Disk 0 Partition 1 as inactive.

Step 1. In the main interface of the MiniTool software, select the partition that you want to activate and click on Set Action from the left panel. Then click on Yes to confirm it.

Step 2. Click on Apply to execute this change. After that, you can check if the MBR2GPT conversion failed error gets fixed.

Solution 3. Repair BCD

As discussed above, corrupted or missing BCD data is also responsible for you cannot find OS partition in MBR2GPT. Let’s follow the steps below to repair it.

Step 1. Press Win + R keys to open the Run box, type cmd in it and press Ctrl + Shift + Enter to open the elevated Command Prompt window.

Step 2. Type the following command and hit Enter to repair BCD.

bcdboot C:\Windows /s C:

Solution 4. Enable WinRE

Some others from the Microsoft forum have proven that enabling WinRE can get rid of the “MBR2GPT cannot find OS partition for disk 0” error as well. It may seem strange but worth trying.

Step 1. Open the elevated Command Prompt window like Step 1 in Solution 3.

Step 2. Type the following commands in order and press Enter after each one.

  • reagentc /disable
  • reagentc /enable

How to fix it if you cannot find OS partition in MBR2GPT? According to the above information, you should find the simplest solution is to use MiniTool Partition Wizard to convert MBR to GPT, right? If other troubleshooting methods can’t fix the MBR2GPT conversion failed error, the MiniTool software is wholly worth trying.

FAQ:

Q: What is Mbr2gpt? 

A: Mbr2gpt is a Windows 10 v1703 and later versions built-in tool that converts a disk from the Master Boot Record (MBR) to the GUID Partition Table (GPT) partition style without modifying or deleting data on the disk.

Q: Why do I need to use Mbr2gpt? 

A: You may need to use Mbr2gpt to switch your PC from BIOS to UEFI mode, which offers better security and performance. You may also need to use Mbr2gpt if you want to use a disk larger than 2 TB, which is the maximum size supported by MBR.

Q: How do I use Mbr2gpt? 

A: You can use Mbr2gpt from a Windows Preinstallation Environment (PE) command prompt or the full Windows operating system by using the /allowFullOS option. You need to run the tool with administrator privileges and specify the disk number and the conversion option. For example, to validate the disk 0 for conversion, you can use the command: mbr2gpt /validate /disk:0 /allowFullOS

Q: What are the advantages of using Mbr2gpt? 

A: You can convert a disk from MBR to GPT without losing data or reinstalling the OS.

You can use a disk larger than 2 TB and create more than four partitions on the disk.

You can enable UEFI mode and benefit from its features, such as faster boot time, secure boot, and device encryption.

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