Changing Back

The lure of the fantasy story is too strong - I have to write this story. So, the aliens will have to wait for their Earth invasion, I'm going back to Ingund.
After talking out my plot with some of the good people on FM, I think I'm getting to the point where I can start writing it. Now all I have to do is get on with it - something that is still not proving as easy as it should.
I just don't know what it is, but as soon as I sit down to write, my mind freezes up. I have managed to force my way through it for a page or so, but not very often. And even then, I fall into the infinite editing loop and wind up going over and over that one page, tweaking here and there, when what I should be doing is carrying on and leaving the editing for later.