Are you in x64 by any chance? If so there is your problem. Not much support for 16 bit in the x64 XP. You might be able to do it in 32bit but doubt it also since XP doesnt have DOS at all just the command prompt. If the game runs from DOS you might be able to do it with compatability but i think that only goes to 98 not DOS.
Did you install something right before they stopped working? that might be your problem there. Try to run it in compatability mode and see if that solves the issue.