Inability to cry?

I guess I tought myself not to cry, and I have not shed a tear in years now, but now as an adult I've had the need to cry and I just cant. I've tried sad songs, books movies and even real life experiences do not help with this matter. It has gotten to the point where I have strong emotions inside me that need to be released, and it hurts me physically not being able to cry. Can anybody give me suggestions as to what kind of things I am doing wrong, or can help me, or at least tell me what helps you??