If these error messages are not available this indicates the corruption of MBR. There may also some illegal message instead of this like, “Your system has been hacked by…..” or any other unexpected message. It indicates that there is something seriously wrong with the MBR, and most probably, it is due to some VIRAL infection
Now check the partition table of MBR after the initial 446 bytes. If the partition table is blank, you will not see any error message at boot time. DOS ignores a non partitioned drive. If there is not any bootable floppy in drive A:, the system will request for a bootable floppy to be inserted in drive A:.
The important thing to be noticed here is that the partition table should not be blank on a drive that was previously working, so something has erased it. If the partition table is blank, restore the MBR from the backup.
If the backup does not work, even after the successful completion of restoring process, there is physical damage on this sector. Try the programming techniques of data recovery, given in the next chapters to recover the data. If you are not a programmer at all, better to go to any good data recovery center.
If you not have any backup of MBR try to write partition table manually with some disk editing tool, like Diskedit, how ever it is very difficult to do so in some cases.
For those users who are not the programmers and also do not have any backup, may use the method which I have been using since my data recovery project development time, in my college days.
What you have to do is, just search the computer near you, which has almost same size of disk, with same number of partitions and the most important thing the same operating system which was in your computer.
However it works completely, most of the time. But if not so, at least it may help you to access the first partition of your disk. Even your operating system will also boot normally, if it was installed in the first partition and if the other information are not corrupted.