cant receive iMessages on iPhone 4s?

Hi I just got my iPhone 4s on Christmas and it was fine then a few months later I could not receive messages at all or open my apps without them cutting off on me and I told the people where I got my phone from and they said that they will figure it out and fix it but it didn't work and now I am still wondering why I cant receive messages or open apps. I also think its because I jail broke it and I uninstalled it without help. SOMEONE HELP MY IPHONE GIVE ME AN ANSWER TO MY SITUATION!!!!! and I already tried the apple support it did not work, talking to a person on apple support did not work. SOMEONE PLEASE HELP ME AND MY PHONE. Also I have the ios 1.7.2