fixmbr device name

Use this command (where device name is an optional device name that specifies the device that needs a new MBR) to repair the master boot record (MBR) of the system partition. This command is used in scenarios where a virus has damaged the MBR and Windows cannot start.
WARNING: This command has the potential to damage your partition tables if a virus is present or a hardware problem exists. This command may lead to inaccessible partitions. Microsoft suggests running antivirus software before using this command.
The name can be obtained from the output of the map command.

If this is left blank, the boot device's MBR is fixed, for example:

fixmbr \device\harddisk2