Writer's Block?

I've had a story in my head, aching to get out, for years now. It's beginning to bother me that, though I love to write, I'm completely at a loss as to how to get this story from my brain to paper. I know the characters (for the most part), I know the setting (I can see it in my mind's eye like it was a photograph being held in front of me), I know the "misunderstanding" that makes the story possible, and I know how it ends. I just don't know the in between stuff and that kills me! Is this considered writer's block? Am I afraid of something? If I'm afraid, what am I afraid of? Maybe I am over thinking this. Maybe what I need to do is not delve directly into details, but get the general story on paper, and then flesh it out...? That's pretty much how I write anyway - and I constantly go back over things and remove what is extraneous and unnecessary and add a word or two here and there to make things more coherent. I do this all after I've already written what I mean to write. Shouldn't the same thing hold true for my story? The other thing is, maybe I'm afraid that what I think is an original idea had been done before. Maybe...but I honestly doubt it. Anyway - I don't really understand what my problem is. This story is pounding at the walls inside my brain so hard that I'm going to wind up with a concussion before long! TTFN JMS