haidee, this is really a long shot, but before you completely abandon trying to solve the problem through Auto Correct, why don't you try creating the exact set of symbols that show up in Word (in error) -- reboot -- and then change them back to "normal." Even though it is clear that you didn't program Word to respond with this weird symbol showing up on your screen, doing this sequence might possibly revert the system to normal.
Very often finding the answer to these kinds of problems becomes a series of investigations, and trial and error. Clearly something has been changed in your system that instructs it to type this strange symbol. So you may have to do some serious digging to figure out exactly what it was.
Another idea that pops into my mind is to do an Advanced Search for the symbol and see what pops up. (Be sure to check "include non-indexed, hidden and system files" and search your entire computer.)
Also, have you looked through all of the symbols in the Symbols link, to see if that symbol is there? If it is, maybe there is a way to delete it.
And my last thought is, have you tried experimenting with Word's "superscript" function, because the way you describe the symbol, it seems as if it's written in superscript.