I am not posting this as a problem for me, but I know how to fix it. It is a rare thing, it has happened to me before. Basically, others can see what your typing, but you can't. This is for WoW, of course. Do the following...
• Get off of World of Warcraft
• "Start", "My Computer", "Local Disc (C", "Program Files", "World of Warcraft".
• Open your "WTF" folder
• Go to "Account", Pick the account the problem occured on
• Pick the realm the problem occured on
• Pick *ALL* of the characters when doing the following..
• Remove the .TXT Document "chat-cache".
Now, this worked for me, no guarentees it will work for you. If you don't understand, please PM me and I will try to explain this a little better.