Repair the Master Boot Record (MBR)

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If the MBR gets damaged, it will render your Windows 8/8.1 computer unbootable. Fortunately, there's a way to repair it and get it working again. This guide will show you how. PCHF recommends you follow each and every step. Skipping a step can render your computer unusable and you'll have no choice but to reinstall the OS.

The following instructions are for Legacy (MBR) installations. If you are booting via UEFI, scroll down the the UEFI instructions.

1.) Insert the installation DVD or Recovery USB flash drive and boot from it.

2.) When the installation screen comes up, select Repair your computer.



3.) At the next screen, select Troubleshoot.

4.) At the next screen, select Command Prompt.

5.) Enter the below commands into the command prompt. WARNING! Any mistake will render your computer useless and you'll have no option but to reinstall Windows 8/8.1 So be VERY CAREFUL.

Code:
bootrec /FixMbr
bootrec /FixBoot
bootrec /ScanOs
bootrec /RebuildBcd

Press ENTER after each command and wait for it to process and finish before proceeding to the next command.

6.) Type
Code:
exit
and restart the PC. Ensure your PC is now bootable.

--------------------------------------------------------------------------------------------------------------------------

The below instructions are for UEFI installations.

1.) Insert the installation DVD or Recovery USB flash drive and boot from it.

2.) When the installation screen comes up, select Repair your computer.



3.) At the next screen, select Troubleshoot.

4.) At the next screen, select Command Prompt.

5.) Enter the below commands into the command prompt. WARNING! Any mistake will render your computer useless and you'll have no option but to reinstall Windows 8/8.1 So be VERY CAREFUL.

Code:
diskpart
sel disk 0
list vol
Press ENTER after each command and let it complete before inputting the next command. These commands will select the first disk of your computer and the list all the partitions available on that disk.

6.) Check for the volume item that has the Fs column FAT32. The EFI partition must be formatted under FAT32. Type the following command:

Code:
sel vol #
where # is the number of the EFI partition.

7.) Assign a letter to this partition, a letter that is unused by any other drive on your computer, for example z:\. To do this, type the following command:

Code:
assign letter=z:
8.) Wait for the following message to appear:

Code:
DiskPart successfully assigned the drive letter or mount point.
9.) Type exit into the command prompt to exit the DiskPart utility.

10.) Type this command and replace z:\ with the letter you assigned earlier to the EFI partition:

Code:
cd /d z:\EFI\Microsoft\Boot\
11.) Type the following command to repair the boot record:

Code:
bootrec /fixboot
12.) Now it's time to backup the old BCD. It's very important to follow this step. Type the following to backup the BCD:

Code:
ren BCD BCD.backup
13.) Now it's time to recreate the BCD. Type the following and replace the z:\ with the assigned letter earlier:

Code:
bcdboot c:\Windows /l en-us /s z: /f ALL
In this command, Windows is installed on c:\. If the drive letter where your Windows 8/8.1 is installed is different, replace c:\ with your drive letter. Also, the /l is a lowercase L, not an I or a number 1.

14.) Remove the DVD/Recovery USB drive, type exit, and reboot.
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