Bootrec /fixboot
To repair the drive’s boot sector, you should use the command “bootrec /fixboot” and reboot the computer.
Bootrec /fixmbr
The “bootrec /fixmbr” command is used to attempt a repair of the master boot record of a drive.
Bootrec /rebuildbcd
The “bootrec /rebuildbcd” command is used to add missing Windows installations to the Boot Configuration Database (BCD).