Welcome to the Community. I am sorry to hear you are having problems with sending text messages let me see if I can get this sorted for you.
If you want to try yourself to resolve the problem feel free to look at our handy Phone Repair tool [Here]
If you still need help then I will need to ask you a few more questions if you don't mind:
What Make and Model handset are you using?
What have you tried so far yourself?
Is it inbound and outbound SMS you are having problems with or just sending?