MBR is damaged
What will happen if the sector signature (last word 0x55AA) has been removed or damaged?
The location of sector signature are overwritten with zeros.
- Physical Sector: Cyl 0, Side 0, Sector 1
- 0000001E0 41 65 0F FE BF 4A 25 83 57 00 66 61 38 00 00 00 Ae.??J%?W.fa8...
- 0000001F0 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 ..............
When trying to boot now, an error message like "Operating System not found" will appear.
Thus, the first thing to do if computer cannot boot is to run a Disk Viewer and check the first physical sector on HDD to see whether it looks like a valid MBR or not:
- Check to see if it may have been filled up with zeros or any other single character
- Check whether error messages (as above - "Invalid partition table"…) are present or not
- Check whether the disk signature (0x55AA) is present or not
The simplest way to repair or re-create a MBR is to run Microsoft´s standard utility called FDISK with a parameter /MBR, as follows.
- A:\> FDISK.EXE /MBR
FDISK is a standard utility included in MS-DOS, Windows 95, 98, ME.
If you have Windows NT / 2000 / XP, you can boot from startup floppy disks or CD-ROM. Choose the repair option during setup, and run the Recovery Console. When you are logged on, you can run the FIXMBR command to fix MBR.
You can also use third party MBR recovery software or if you´ve created a MBR backup, restore it from there (Active@ Partition Recovery has such capabilities).
See also:
What will happen if the first sector has been damaged (by virus, for example)?