This happened to me too. For some reason, the WoW installation reset itself and brought me back to the terms of agreement. I found a fix on Blizz forums that summarizes as follows.
1. Go to your WoW installation
2. Go to the WTF folder
3. Your login name folder
4. Nostalrius PVE folder, or your server folder
5. Your character name folder
6. Delete the chat-cache file. It holds the variables for your chat settings. It got corrupted during a reset. Don't worry, WoW will create a default one on start.
