Fix: The Selected Disk is not a Fixed MBR Disk

This error appears when trying to set mark a partition on a disk as active either by using Disk Management or DiskPart. The error message appears along the following lines:

The selected disk is not a fixed MBR disk.
The ACTIVE command can only be used on fixed MBR disks.

This problem indicates that the disk where the partition you want to mark as active is located as a GPT (GUID partition table) disk. This is tightly related to UEFI boot specifications instead of BIOS and this boot method doesn’t recognize a concept such as an active partition.

The Selected Disk is not a Fixed MBR Disk

There are several things you can do in order to resolve the problems simply by following the methods we have prepared below.

What Causes the “The Selected Disk is not a Fixed MBR Disk” Error Message?

Identifying the correct cause of the problem is one of the most important steps used to actually resolve it. Check out the list below to see the most common causes and how to resolve them:

  • The problem is often simply caused by the fact that the drive where you want to add a primary partition or set a partition as active is formatted as GPT which doesn’t support these features. Changing its format to MBR should resolve the problem.
  • Boot manager problems can also cause the error message to appear and this can be resolved by running several useful commands used to fix it.
  • If your boot mode is set to UEFI, you might want to consider changing it to Legacy as this has resolved the problem for many users.

Solution 1: Convert the Disk to MBR

Since a disk formatted as GPT doesn’t recognize a concept such as an active partition, you can simply convert to disk to MBR which will effectively resolve the problem. After this, you will be able to create a primary partition and mark it as active. However, make sure you back up the data from the disk as it will be deleted.

You can use Command Prompt and DISKPART to clean the drive entirely and convert it to MBR easily.

  1. If your computer’s system is down, you will have to use the installation media used to install windows for this process. Insert the installation drive you own or which you have just created and boot your computer.
  2. You will see a Choose your keyboard layout window so choose the one you want to use. The Choose an option screen will appear so navigate to Troubleshoot >> Advanced Options >> Command Prompt.
Command Prompt in Advanced Options
  1. At this command prompt window, type in simply “diskpart” in a new line and click the Enter key in order to run this command.
  2. This will change the Command Prompt window to enable you to run various Diskpart commands. The first one you will run is the one which will enable you to see the complete list of all available volumes. Type this in and make sure you click Enter afterward:
DISKPART> list
  1. Make sure you choose your drive carefully, depending on which number is assigned to it in the list of volumes. Let’s say that its number is 3. Now run the following command in order to select your USB drive:
DISKPART> select volume 3
  1. A message should appear saying something like “Volume 3 is the selected volume”.
Selecting the proper volume

Note: If you are unsure about which drive number belongs to your USB device, the easiest way to do so is to check its size at the right pane.

  1. In order to clean this volume, all you need to do is to type in the command displayed below, click the Enter key afterwards, and stay patient for the process to complete. The process should now be successful for a change. The set of commands will also convert the disk to MBR and hopefully resolve the problem.
Clean
Convert MBR 
Exit

Solution 2: Fix the Boot Manager

Going through the essential commands related to the boot manager is always a nice and easy way to get started with your troubleshooting. There are several methods you should run in a particular order in order to reset and reboot the Boot Manager service which is directly responsible in managing the drives connected to your computer.

  1. If your computer’s system is down, you will have to use the installation media used to install windows for this process. Insert the installation drive you own or which you have just created and boot your computer.
  2. You will see a Choose your keyboard layout window so choose the one you want to use. The Choose an option screen will appear so navigate to Troubleshoot >> Advanced Options >> Command Prompt.
Command Prompt in Advanced Options
  1. If you are not having problems with the system, you can use the Windows UI to access this screen. If you are using Windows 10 on your PC, there is another way to access the Advanced Startup on your computer. Use the Windows Key + I key combination in order to open Settings or click the Start menu and click the gear key at the bottom left part.
  2. Click on Update & security >> Recovery and click the Restart Now option under the Advanced startup section. Your PC will proceed to restart and you will be prompted with the Advanced options screen.
Restart Now in Settings
  1. Click to open the Command Prompt from the Advanced options screen.
  2. Command Prompt should now open with administrator privileges. Type in the command displayed below and make sure you hit Enter afterwards.
bootrec /RebuildBcd
bootrec /fixMbr
bootrec /fixboot
  1. Close Command Prompt afterwards and choose the Restart option. Check to see if the problem is gone.

Solution 3: Disable UEFI in BIOS

Since GPT is closely related to UEFI boot mode, you should try and disable UEFI from the boot menu and switch it to legacy. This has resolved the problem for some users. Make sure you follow the instructions carefully!

  1. Turn your PC on again and try to enter BIOS settings by pressing the BIOS key as the system is about to start. The BIOS key is typically displayed on the boot screen, saying “Press ___ to enter Setup.” or something similar to that. There are other keys as well. The usual BIOS keys are F1, F2, Del, etc.
Press __ to run Setup
  1. Use the right arrow key to choose the Security menu when the BIOS settings window opens, use the down arrow key to select the Secure Boot Configuration option, and press Enter.
  2. Before you can use this menu, a warning will appear. Press F10 to continue to the Secure Boot Configuration menu. The Secure Boot Configuration menu should open so use the down arrow key to select Secure Boot and use the right arrow key to modify the setting to Disable.
Disable Secure Boot in BIOS
  1. Now it’s time to change the boot mode from UEFI to Legacy. The Boot Mode option which you will need to change is located under different tabs on BIOS firmware tools made by different manufacturers and there is no unique way to find it. It’s usually located under the Boot tab but there are many names for the same option.
  2. When you locate the Boot Mode option in any area of the BIOS settings screen, navigate to it and change its value to Legacy.
Switch from UEFI to Legacy mode
  1. Navigate to the Exit section and choose to Exit Saving Changes. This will proceed with the computer’s boot. Check to see if the problem persists.

Kevin Arrows


Kevin is a dynamic and self-motivated information technology professional, with a Thorough knowledge of all facets pertaining to network infrastructure design, implementation and administration. Superior record of delivering simultaneous large-scale mission critical projects on time and under budget.

Expert Tip

Fix: The Selected Disk is not a Fixed MBR Disk

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