I know the exact feeling as I am going througha turmulous, chaotic and sad time in my life right now and am also unable to cry.

I have a theory, however. (Take this with a grain of salt, as I am by no means a psychologist yet.)

I believe that, at some point, we just get "Cried out". In other words, our minds become sort of... cauterized to the feeling. Even though we feel better when we cry, we've either done it so much, or have been raised in a certain way that crying becomes alien to our minds.

Anyway, that's what I think, take it with as much salt as you'd like.

Thanks~
Samuel Cross-Meredith