I have full service but all my messages refuse to send? Yesterday I encountered a problem with my phone: I have full service and I can make phone calls, download, and use internet without a problem. I can also receive messages, but anytime I try to send it seems as if it doesn't even make an effort trying to send. It instantly says 'message not sent'. I have factory reset my phone 3 times since then. 

I can't figure out what could cause this....its really frustrating...please help.
This sounds like your SMS settings are wrong. Most likely the SMSC (Short Message Service Center) number is not set. Check your settings with the one your provider/carrier tells you to set.