Use the following commands:
Sys
srcboot
bootpart
attrib
Specific steps are:
1. Boot Dos with a CD or floppy disk;
2. Sys a: c: (Transfer DOS boot files so that the existing C: drive can boot DOS);
3. Srcboot c: c:\bootsect.dos /s (Save the current DOS boot information);
4. Echo y|Bootpart winnt boot:c: (This step is to re - restore the Nt boot kernel because you used Sys a: c: to overwrite the original Nt boot information on the C: drive. If this step is not carried out, booting from the hard disk will become pure DOS);
5. Attrib -h -s -r C:\boot.ini (This step is to remove the hidden, system, and read - only attributes of Boot.ini);
6. Echo c:\="MS-DOS">>c:\boot.ini (Add an option to enter DOS in Boot.ini);
7. Attrib +h +s +r C:\boot.ini (Restore the hidden, system, and read - only attributes of Boot.ini);
8. Restart the computer, press F8, select the last item "Return to the operating system selection menu", and select the "Ms-dos" item to be able to enter pure DOS.