Start partition magic, select a physical disk listed in the main window, select from top menu Disk -> Rebuild MBR.
If MBR (Master Boot Record) of disk is damaged, system cannot boot. This feature will rewrite the Master Boot Record of the selected disk without destroying the disk partition table.
What is MBR?
A master boot record (MBR), or partition sector, is the 512-byte boot sector that is the first sector ("LBA Sector 0") of a partitioned data storage device such as a hard disk. (The boot sector of a non-partitioned device is a Volume Boot Record. These are usually different, although it is possible to create a record that acts as both; it is called a multi boot record.) The MBR may be used to hold a disk’s primary partition table. The MBR is not located in a partition; it is located at a Main Boot Record area in front of the first partition.