BOOTREC.exe (Windows RE)

Repair or replace a partition boot sector.

Syntax 
 BOOTREC /FIXMBR Write a Master Boot Record (MBR) to the system partition.
 BOOTREC /FIXBOOT Write a new Boot Sector onto the system partition.
 BOOTREC /SCANOS Scan all disks for Windows installations and display entries
 not currently in the BCD store.
 BOOTREC /REBUILDBCD Scan all disks for Windows installations and provide a choice of
 which entries to add to the BCD store.

/FixMbr does not overwrite the existing partition table. Use this option when you must resolve MBR corruption issues, or when you have to remove nonstandard code from the MBR.

Use /FixBoot if The boot sector was damaged or replaced.

Examples

Fix the MBR and boot sector:

C:\> bootrec.exe /fixmbr
C:\> bootrec.exe /fixboot
C:\> bootrec.exe /rebuildbcd

Then Reboot.

Rebuild the BCD store

C:\> BOOTREC /REBUILDBCD

Troubleshoot a "Bootmgr Is Missing" error.
If rebuilding the BCD store doesn’t resolve the startup issue, you can export and delete the BCD store and then run this option again. By doing this, you make sure that the BCD store is completely rebuilt. To do this, type the following commands at the Windows RE command prompt:

bcdedit /export C:\BCD_Backup
c:
cd boot
attrib bcd -s -h -r
ren c:\boot\bcd bcd.old
bootrec /RebuildBcd

"If you want a picture of the future, imagine a boot stamping on a human face — forever" ~ George Orwell (1984)

Related commands

BCDBOOT - Create or repair a system partition.
BCDEDIT - Manage Boot Configuration Data.
SYSPREP - (Generalize) a Windows installation.
WPEUTIL - Run commands during a Windows Preinstallation Environment (WinPE) session.
Windows Recovery Environment (WinRE), Safe mode and Win PE.