World of warcraft..please help!!?

i have a character, that all of a sudden cant see speech. like i can see the speech bubbles, but as far as coming up on the bottom of my screen i cant; for example- people cant whisper to me as it doesn't come up on the bottom, and when im in a city, instead of the usual banter from everyone..i have nothing. its really annoying as communticating in dungeons etc is crucial and i cant do it. have i changed an option on the interface and is there anything i can change to make it re-appear? any advice welcome....thanks x)