In some situations such as a virus attack, power surge, etc, Master Boot Record can get damaged. Due to this damage the computer becomes un-responsive and unbootable.
If a Master Boot Record and partition information backup is available on a floppy drive, then you can recover and restore Master Boot Record using Active@ Partition Recovery.
Boot the machine using that floppy and run Active@ Partition Recovery and restore Master Boot Record from the backup.
IT IS STRONGLY ADVISED TO MAKE MBR AND PARTITIONS BACKUP EVERY TIME THE COMPUTER CONFIGURATION IS CHANGED ( SUCH AS ADDING/REMOVING HDDs, PARTITIONS, LOGICAL DRIVES).