The Master Boot Record (MBR) is a special type of boot sector found at the beginning of your system partition. The MBR informs the boot process as to what is about to follow, such as partition layouts, sizes, file systems, and so on. An MBR also traditionally contains a small piece of executable code that passes the boot process to the operating system proper, landing you within Windows.
Causes of Startup Failure in Windows 10
A master boot record corruption can happen for a number of reasons. Drive failure and damage is a very common cause. In recent years, certain ransomware variants attacked the master boot record to force victims into paying to secure their system. Thankfully, this ransomware practice is rare, though numerous other malware examples directly alter the MBR for maximum damage and irritation.
That said, there are several effective ways to fix the Windows master boot record. If one fix doesn’t work for your system, try the next.
1. Startup Repair via Windows Automatic Repair
When you first boot your Windows 10 system, it should detect that there is an issue and enter Automatic Repair mode. The screen reads Your PC did not start correctly. From here, select Advanced options > Troubleshoot > Startup Repair.
The Windows 10 Startup Repair tool is completely automated. It does, however, take a long time to complete, but it should fix your Windows 10 MBR issues.
2. Command Prompt via Windows Automatic Repair
If the Windows 10 Startup Repair process doesn’t fix your MBR issue, or you simply prefer a faster, more direct approach to fixing your system, you can use the Command Prompt via Automatic Repair. When your system detects there is an issue and the Automatic Repair screen appears, select Advanced Options > Troubleshoot > Command Prompt.
You are going to use the bootrec.exe tool to repair the corrupt MBR. Bootrec has a range of commands designed to recover the boot process from issues and is already on your Windows 10 system as part of the base installation.
Type bootrec.exe /fixmbr and press Enter. Then type bootrec.exe /fixboot and press Enter. You should see The operation completed successfully underneath each command. If you don’t see the operation completion message and instead receive an error, enter bootrec.exe /rebuildbcd and press Enter. The “rebuildbcd” command attempts to rebuild your system Boot Configuration Data (BCD).
Unfortunately, this doesn’t always work the first time around. In this case, Microsoft suggests exporting the BCD store (the place your boot data is kept) and completely rebuilding from scratch. Sounds scary, but it only takes a short moment.
Enter the following commands in order:
bcdedit /export c:\bcdbackup c: cd boot attrib bcd -s -h -r ren c:\boot\bcd bcd.old bootrec.exe /rebuildbcd
The export and rebuild process should completely repair your MBR issues.
Those users still working with Windows 7 or an earlier version can also use the bootrec.exe /scanos command. This command scans for and repairs legacy BCD settings.
If You Can’t Access Command Prompt via Automatic Repair
Some users will find that Windows 10 Automatic Repair doesn’t appear at the desired moment. In this situation, you need to use your Windows installation media to boot into repair mode.