Well, this will either help or reveal me as a nutball, but I 'see' everything like a movie, then just write down what I see and hear. The only time I've been stuck is when 'I' get in the way of the story and try to put things in that I want to see happen. The best dialog has also been the stuff I've just heard. People talk to me in the shower-lol!
Someone further up also had good advice- write the end first. I co-wrote my first novel was done that way. We saw the beginning and the end and all we had to do was figure out how I could logically get from one point to the other.
It's also nice when things just write themselves, coming so quickly and smoothly that its like taking dictation. I've heard people say that art, like writing and music etc, comes THROUGH us not from us. In at least one case I can tell you that that is true.
Good luck. Back away. Try another perspective- and listen.