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Damaged MBRs and Boot Sectors

When you start a computer from the hard disk, the system BIOS code identifies the startup disk and reads the MBR. The master boot code in the MBR searches for the active, primary partition on the hard disk. If the first hard disk on the system does not contain an active partition, or if the master boot code cannot locate the system partition's boot sector to start the operating system, the MBR displays one of the following error messages:

Invalid partition table.

Error loading operating system.

Missing operating system.

There might not be an active partition on the hard disk that you want to use to start the computer, or the wrong partition might be identified as the active partition. In this case, use an MS-DOS startup floppy disk to start the computer and use the MS-DOS tool Fdisk to set or change the active partition.



Fdisk can only set primary partitions as the active partition. If MBR corruption prevents Fdisk from setting or changing the active partition, you might need to use a third-party, low-level disk editor that can work under MS-DOS to make this change manually. The partition table field that needs to be changed is the System ID field. For more information about the fields in the partition table, see "Master Boot Record" earlier in this chapter.

Using an Emergency Repair Disk

If the boot sector cannot find Ntldr, Windows 2000 cannot start. This can be caused by moving, renaming, or deleting Ntldr, corruption of Ntldr, or corruption of the boot sector. Under these circumstances, the computer might not respond to input or might display one of the following error messages:

A disk read error occurred.

NTLDR is missing

NTLDR is compressed.

If Ntldr is damaged or missing, or if the boot sector is corrupted, you can resolve either problem by starting the Emergency Repair Disk (ERD) and following the prompts for repairing the installation. For more information about the ERD, see Windows 2000 Server Help.

Using the Recovery Console

If the system cannot start due to a corrupted MBR or boot sector, you can recreate either of these disk structures by using the Recovery Console.

To start the Recovery Console, start the computer from the Windows 2000 Setup CD or the Windows 2000 Setup floppy disks. If you do not have Windows 2000 Setup floppy disks and your computer cannot start from the CD, use another Windows 2000–based computer to create the setup disks. For information about creating the Windows 2000 Setup floppy disks, see Windows 2000 Server Help.

Start the computer and enter Windows 2000 Setup. Press ENTER at the Setup Notification screen to go to the Welcome to Setup screen. Press R to repair a Windows 2000 installation, and then press C to use the Recovery Console.

The Recovery Console displays all valid installations of Windows 2000 on the computer. To access the hard disk, press the number key representing the Windows 2000 installation you want to repair (typically represented as 1: C:\WINNT), and then press ENTER.



If you press ENTER without typing a number, the Recovery Console quits and restarts the computer.

The Recovery Console may also show valid installations of Windows NT. However, as the Recovery Console was not specifically designed to work with Windows NT, the results of attempting to access a Windows NT installation can be unpredictable.

The Recovery Console then prompts you for the Administrator password.



To access the hard disks with Recovery Console, you must know the password for the local Administrator account. If you do not have the correct password, or if the security database for the installation of Windows 2000 you are attempting to access is corrupted, Recovery Console does not allow access to the local disks.

To replace the MBR, at the Recovery Console command prompt, type:


Verify if you want to proceed because depending upon the location and the cause of the corruption within the damaged MBR, this operation can cause the data on the hard disk to become inaccessible. Press Y to proceed, or N to cancel.



Running Fixmbr overwrites only the master boot code, leaving the existing partition table intact. If the corruption in the MBR affects the partition table, running Fixmbr may not resolve the problem.

To have the Recovery Console replace the boot sector, at the Recovery Console command prompt, type:


If you do not specify a particular drive, the Recovery Console replaces the boot sector of the boot partition. If another volume's boot sector is corrupted, enter the Fixboot command, followed by a space, and then specify the drive letter with a colon immediately afterward.

You can also use DiskProbe to edit these disk structures. Because DiskProbe only runs under Windows 2000 and Windows NT, you can only use it to fix errors on a boot sector, a non-startup partition, or an MBR on a non-startup disk. For more information about using DiskProbe to edit boot sectors and MBRs, install the Support Tools from the Windows 2000 Setup CD and see the document Dskprtrb.doc.

For more information about the Recovery Console, see "Repair, Recovery, and Restore" in this book.