You might see one of the following error messages when you have configured your x86-based computer to dual-boot Windows NT and MS-DOS:
Non-System disk or disk error
Replace and press any key when ready
– Or –
Couldn't open boot sector file
multi(0)disk(0)rdisk(0)partition(1):\Bootsect.dos
These error messages occur because the Bootsect.dos file is missing or corrupt. Bootsect.dos is a hidden, system, read-only file that NTLDR uses to start the MS-DOS operating system.
Because Windows NT is able to load correctly and the Partition Boot Sector is not damaged, the Emergency Repair Disk might not detect a problem. To force the Emergency Repair Disk to rewrite Bootsect.dos, you should use the following procedure.
1. Shut down and restart the system from an MS-DOS startup floppy disk that contains the MS-DOS program Sys.com. Type sys c: at the command prompt.
You should receive a System Transferred message. Sys.com replaces the Partition Boot Sector, which loads NTLDR, with an MS-DOS Partition Boot Sector that loads Msdos.sys and Io.sys.
2. Start the computer from the Windows NT Setup disk 1. Insert disk 2 when it is requested. When prompted, select the option to Repair by entering R. Setup displays the following options:
[X] Inspect registry files
[X] Inspect startup environment
[X] Verify Windows NT system files
[X] Inspect boot sector
Continue (perform selected tasks)
3. Clear all selections except Inspect boot sector. Select Continue (perform selected tasks).
4. After disk 3, you will be prompted for the Emergency Repair Disk. Setup displays the following messages after it has finished processing the Emergency Repair Disk:
Setup has completed repairs.
If there is a floppy disk inserted in drive A:, remove it.
Press ENTER to restart your computer.
The Repair process replaces the Partition Boot Sector and creates Bootsect.dos so that the dual-boot configuration is restored.