Sometimes due to one of the many reasons (virus attack, power surge ...) MBR damage can occur. It makes computer un-responsive, and you are not able to boot/start your machine.
If you have made a backup of your MBR and partition information to a floppy drive, then using Active@ UNERASER you can virtually restore MBR and copy all important data to another drive.
Just boot your machine from bootable floppy, run Active@ UNERASER and restore MBR from the backup.
See "How to make backup and restore of MBR, Partition Table and Boot Sectors?" topic for details.