Eazy,
I have sort of the same problem. When I've worked forever on a script, the "oh, this is a fantastic idea!" starts to fizzle out after awhile, and then I stop writing it completely. The problem was that I was trying too hard to make it perfect, starting from begining and trying to work my way through to the end, often times spending hours on one page alone.
This is what I do now. Before I begin I use index cards to write down each scene, its goal, and a brief discription of what happens. Everyday I take a few random cards and write out the scenes. I don't even think of the story as a whole yet, (okay, maybe a little), but the idea is not to be intimidated on how much you still need to write and just concentrate on a little bit at a time. I work on each scene like it's an individual piece, a mini-mini-story. Then when they are all done, I will go over it as a whole and fix any kinks, then begin my rewrite. Remember most of the work in writing is revising and rewriting. Your first draft is going to be far from perfect no matter who you are. So take your time, have fun, learn all that you can, and don't give up!
Steph