Microsoft KB Archive/102793

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Unable to Load MS-DOS with Windows NT OS Loader

Article ID: 102793

Article Last Modified on 11/1/2006


  • Microsoft Windows NT Advanced Server 3.1
  • Microsoft Windows NT Workstation 3.1
  • Microsoft Windows NT Advanced Server 3.1

This article was previously published under Q102793


If BOOTSECT.DOS is corrupt, the MS-DOS operating system may be unavailable and one of the following error messages may be received when MS-DOS is selected from the OS Loader Menu during startup:

Non-System disk or disk error
Replace and press any key when ready

Couldn't open boot sector file


These error messages are caused by a missing or corrupt BOOTSECT.DOS file. BOOTSECT.DOS is a hidden, system, read-only file used by NTLDR to start the MS-DOS operating system.


Because Windows NT is able to load correctly and the boot sector itself is not damaged, the Emergency Repair Disk may not detect a problem. To force the Emergency Repair Disk to rewrite the boot files, the following workaround must be used.

NOTE: The Windows NT Emergency Repair Disk must be available and working correctly for the following procedure to succeed. To test the Emergency Repair Disk, press the SPACEBAR key when you are prompted while Windows NT is loading. The Repair menu should appear.

  1. Load Windows NT and use File Manager to back up the Emergency Repair Disk and any critical data before proceeding.
  2. Shut down and reboot the system to a bootable disk that contains the MS-DOS program SYS.COM.
  3. From the bootable disk in drive A, use the following command to remove the Windows NT boot sector:

          SYS C:

    You should receive a "System Transferred" message.

    SYS.COM replaces the partition boot sector, which loads NTLDR, with an MS-DOS boot sector that loads MSDOS.SYS and IO.SYS.

  4. Reboot the system with the Windows NT Setup Disk number 1 in drive A. When prompted, type R for Repair. Setup will then prompt for the Emergency Repair disk, read data from it, and prompt again for the Setup disk to be inserted in drive A.
  5. The Windows NT Setup menu will be displayed. Select only Verify Boot Files on drive C. Highlight Continue (perform selected Tasks) and press ENTER.

    After Setup rebuilds the damaged files, you will be prompted to reboot the machine.

The Repair process will replaces NTLDR, NTDETECT.COM, BOOTSECT.DOS, BOOT.INI, and the partition boot sector so that the original dual-boot configuration will be restored.

Additional query words: prodnt tshoot dual boot repair

Keywords: kbother KB102793