If you are running the Windows 3.x it is likely that the computer might be booting into the Windows automatically and bypassing in the MS-DOS prompt. If Windows loads successfully into Windows, if you wish to exit to a MS-DOS prompt, from Program Manager, then click the File menu and click at the Exit option.

If still the computer is trying to load the Windows but is encountering errors while it is booting, reboot your computer and press the F5 key from the keyboard when you see the message displaying as "Starting MS-DOS" or the MS-DOS version. This will enable you to load with the default standard of MS-DOS in the computer.
If you do not wish Windows 3.x to load automatically into your operating system, you will need to file and remove then "win" line.