The partition's first sector is also known as the boot sector. What the MBR is for entire drive, that the boot sector is for an individual partition: like the MBR, the boot sector contains information that the system needs to locate the materials that are needed to start the operating system. A corrupt or missing boot sector is a serious problem. Without it the partition can not be accessed.

Possible (but not all) symptoms are:
Invalid media type reading drive
Abort, Retry, Fail?
File system is displayed as 'RAW'
Windows may ask if you want to format the drive
File names contain 'weird' characters
'Sector not found' messages

If boot sector of one FAT16/FAT32/NTFS partition was corrupt, it will be marked with ' X ' by Partition Table Doctor.

If you cannot access the FAT16/NTFS partition and the partition was marked with ' X ', right click the partition and choose Fixboot. Partition Table Doctor will automatically check and repair the boot sector of the partition.

If you cannot access the Fat32 partition and the partition was marked with ' X ', right click the partition and choose Fixboot. There are two choice :

'Auto' mode: Partition Table Doctor will automatically check and repair the boot sector of the partition. We recommend you choose this mode. If 'Auto' mode doesn't work, you could choose 'Interactive' mode. You must input the Label for the partition or file name (the file is in the Root Folder). If you do not know what file name to input, follow the file name that is suggested:

Bootable partition:
io.sys   msdos.sys  ntldr  bootlog.txt
Other partitions:
_restore recycled

File name cannot support long name or wildcard character by DOS version of Partition Table Doctor.

Browse : In both of the modes, Partition Table Doctor will provide you a preview of the folders and files in the root directory on this partition before 'Yes' option being chosen to make the change valid on a dialogue box. If it appears the same as the previous one that means this function can fix it.