Umm, before you try 486 player's rather ... err extreme "solution"

You may want to look at your SYSTEM.INI file ...
Open the Run box and type "sysedit". An app will open with several system files in windows, click SYSTEM.INI. Look for the "KEYBOARD=" line that is mentioned in the file. You don't mention what OS you are running, but I have WinXP and I don't have any KEYBOARD= line in my SYSTEM.INI. If you wanted to try removing that line (not sure what that line DOES so if you do this, anything that happens is not my fault

) you can put a semicolon ; in front of it to comment it out. Then reboot and see if DOS works ...
Alternatively, you could download DOSBox, a free MS-DOS emulator, from:
http://dosbox.sourceforge.net
You can use that instead to run DOS programs and it often works better than the default DOS prompt.