Nokia 6085 - my Nokia won't send text messages?

I have had my Nokia for at least a year, and have had no trouble with it at all, but just last week it won't let me send messages, but I am still receiving messages. All my sent messages say they are being sent, and are in my Outbox, but they just sit there and never actually send.

Does anyone know what this is, or how to fix this problem?
Thanks