if NTDS.DIT file is corrupted, deleted or missing you should restore it like any other regular file.
To restore NTDS.DIT from backup,use this method:
1. Reboot your domain controller.
2. Press F8 when comnputer loads to get into the windows menu.
3. Select directory services restore mode.
4. Login to directory services restore mode using administrator credentilas.
5. Go to Start < Programs > Accessories > System Tools > Backup.
6. Select the Restore tab.
7. Click "+" button to expand: File > Media Created > System Drive Winnt > NTDS
8. Mark the check box to select the NTDS.DIT file
9. Leave the Restore Files To box set to Original Location. If restoring an alternate
location, copy the NTDS.DIT file to the location where it should be.
10. Click Start Restore.