I have come across this problem about ten times in the last ten years, and it is more complicated than this user discovered. I'm in Word 2003 now, but it has also happened in earlier versions of Word.There is some key combination which can be struck inadvertently that changes all newly entered keystrokes into ALL CAPS (although the Caps Lock light is not on) and changes lots of other functions--cut and paste works differently, toolbar categories have changed-- -"Save" is now "Save All," "Close" is "Close All" etc. Backing up and deleting doesn't fix it, leaving Word and coming back in doesn't do it. It doesn't just affect the file in which it happens. If I close that file and go into another Word file, the new file will be in this Weird Mode--any new typing will be all caps. But if I turn off the computer and turn it back on, it reverts to normal Word. I've asked college classes if this has ever happened to anyone else, and I sometimes find one other person who says that it has happened to them, and they found it just as inexplicable.
It seems to happen with the left hand, which leads me to believe that the Caps Lock button is involved (but it isn't just that). If I hit the Caps Lock button when in the Weird Mode, the Caps Lock light comes on and everything goes into lower case.
Any ideas? I can't really experiment with it, because I don't know how to get into the Weird Mode.