Brick Walls

Can someone please explain to me why there are times when you sit down to write and it is like facing a brick wall and not a computer screen? I have hit one of those moments. I got all my work out of the way today with the plan to use some of the inspiration I had gained in Normandy. I have two notebooks full of ideas and thoughts (not just Normandy) plus 250+ photos. I know where the story has to go. So I should be able to sit down and write, shouldn't I?
what actually happens is the brain becomes 'constipated' - sorry but is the only way to describe how each word is forced painfully onto the screen and even as you type it you know it is not right. It doesn't say what you want it to.
My solution has been to walk away. Think some more. Go through my notes and read what I have written so far. Perhaps this is the punishment for having two novels on the go which are at different age groups. Who knows! But the thing I do know is that I have to have the first draft of the novel written by the end of the summer. I have 26K down and probably another 40K or so to write. I need to stop wittering and get writing.
Tomorrow I will return to it and tomorrow everything will flow freely....I hope it.

If the computer would let me I would place a link to Pink Floyd's Another Brick in the Wall, unfortunately it won't let me so you will have to hum it...ready? humm hummm