Htc evo 4g help with messages?

I have an htc evo 4g and it just recently it deleted ALL of my messages. it did it again today, and I do not have my settings under "Delete old messages." I didn't have 1000+ messages, not even 300 this time. I've had this phone since x-mas. I don't know what to do. I read the manual... How can I make this stop. It also deleted my locked messages. PLEASE HELP