1) Type "exit" at the command prompt.
2) If you still get the same error, try edit the file "config.sys" by typing the following command at command prompt:
"edit c:\config.sys" and remove the line "DOS=SINGLE" if there is.
3) If the above steps do not help, you will need to reinstall Windows 98 by running the "setup.exe" file in the following location:
4) If the same error still exists, you will need to recover the system using the Recovery CD provided.