Master Boot Record (MBR), sometimes also referred to as the “master partition table” or “partition sector”, is the most important piece of information that enables your PC to find and identify the location of the OS to allow Windows 10 to boot.
Often due to viruses, system reconfiguration, or when your computer doesn’t shut down properly can cause the Master Boot Record to get corrupted, and sometimes you may even come across the Bootmgr Is Missing error that will prevent your device from booting.
If you ever have such a problem, you’ll need to fix the MBR to enable Windows 10 to load again using a bootable installation media and Command Prompt.
How to repair the Master Boot Record
To fix problems with the Master Boot Record on a device running Windows 10, use these steps:
Change your device BIOS settings to start from the bootable media. (This process usually requires to press one of the function keys (F1, F2, F3, F10, or F12), the ESC or Delete key. For more accurate instructions, visit your PC manufacturer’s support website.)
Start your computer with the bootable media to boot into the Windows 10 Setup.
Click the Next button.
Click the Repair your computer button in the lower-left corner.
Click the Troubleshoot button.
Click the Advanced options button.
Click the Command Prompt button.
You’ll now enter into the Command Prompt environment, which will allow you to launch the Bootrec.exe tool to repair the Master Boot Record on your Windows 10 PC. Bootrec.exe supports a number of options depending on your situation.
Use the FixMbr option when you need to repair Master Boot Record corruption problems, or when you need to clean the code from the MBR. This command will not overwrite the existing partition table in the hard drive.
Use the FixBoot option when the boot sector was replaced with another non-standard code, the boot sector is damaged, or when you installed an early version of the operating system alongside another more recent version.
Use the ScanOS option when the Boot Manager menu doesn’t list all the operating systems installed on your computer. This option will scan all drives to find all compatible installations and it will display the entries that are not in the BCD store.
Use the RebuildBcd option when you don’t have another option and you must rebuild the BCD (Boot Configuration Data) store.
If you are trying to troubleshoot a “Bootmgr Is Missing” error and rebuilding the BCD store doesn’t fix the problem, you can use the following commands to export and erase the BCD store and using the RebuildBcd command again to try getting Windows 10 to boot.
While in the Command Prompt using the recovery environment, type the following commands and press Enter on each line:
BCDedit /export C:\BCD_Backup C: CD boot Attrib BCD -s -h -r Ren C:\boot\bcd bcd.old Bootrec /RebuildBcd
Press Y to confirm adding Windows 10 to the list of bootable operating system on your computer.
Close Command Prompt.
Once you’ve completed the steps, reboot your devices, and then, you should now be able to load Windows 10 again.
If you are not sure exactly what’s the problem with your computer, you should try all the commands in this guide to see if any of them repair the issue allowing you to boot again into Windows 10.
While Bootrec.exe should be good enough to repair the Master Boot Record, there are other related issues that may require the use of other command line tools, such as Bootsect.exe or BCDboot, but they are beyond the scope of this guide.
Were you able to fix the Master Boot Record problem on your Windows 10 PC? Let us know in the comments.
Update August 21, 2018: Originally published in May 2016, revised in August 2018.