I suggest that you choose MS-DOS and then rename both the Config.sys
file and the Autoexec.bat file. For example,
   ren config.sys config.syz
   ren autoexec.bat autoexec.baz

If you cannot get into MS-DOS, then make a Windows Startup Disk (or
use one you made earlier), and put this Startup Disk in drive A:
before you turn on the computer. You can obtain a Windows Startup Disk
at:
           http://www.bootdisk.com/
Then you should be able to rename the Config.sys file and the
Autoexec.bat file.

If you can get into MS-DOS, use DOS commands to make backups of any
files you cannot afford to lose. For example, spreadsheets, letters,
address lists. There is a chance that the computer hardware is failing
or has failed.

If the above steps allow you to start Windows in Safe Mode, you'll
need to figure out what you did that caused this trouble in the firstn
place. One conjecture would be that you installed some software
(probably a game) that messed up the Config.sys file. I would
uninstall anything installed just before the trouble began.

If the above steps do not work, I'd try reinstalling Windows. For this
purpose, you will need to have access to the CD-ROM from DOS, which
implies that you will need very basic Config.sys and Autoexec.bat
files. I would not use the versions of these files that are on the
harddisk not because the error message may imply that something is
wrong with these files. I suggest that you leave the current files
renamed (as above) and that you create new ones with just one line in
each file.

Here is how to add your CD-ROM driver to the boot disk. The boot disk
might be drive C: or it might be a Windows Startup Disk that you can
insert into drive A:.

The CD-ROM driver will normally have a name with the letters CD in it
and it will have the extension .SYS. One way to get a CD-ROM driver is
to run the installation program that came with the CD-ROM. Also, you
can usually get a driver from the web site of the companmy that made
the CD-ROM. Or you can search your C: drive for *CD*.SYS.

Using Notepad or any word processor, make a text file, name it
CONFIG.SYS and add it to the boot disk.  This file should look like
this, but with the name of your CD-ROM driver in place of
CDDRIVER.SYS:
DEVICE=CDDRIVER.SYS /D:MSCD000
DEVICE=HIMEM.SYS

Add a copy of MSCDEX.EXE to the boot disk. You can get MSCDEX from the
folder C:\Windows/Command.

Using Notepad or any word processor, make a text file, name it
AUTOEXEC.BAT and add it to the bootdisk.  It should look like this:
MSCDEX.EXE /D:MSCD000

If none of the above works, talk with tech support at the company that
made the computer.

Bill Starbuck (MVP)