I've noticed that I have an incredible inability to focus and complete tasks that are more than brief.
For example, I can't write code for my own projects. I'm sure part of that is because of having a day gig, sure, but it annoys me to no end. So much of what I'd like to do on my sites is contingent on getting my f'ing forum rewritten, and I can't sit down to just make it happen. It really bothers me.
I'm having some problems writing my short film too, but that's more because I keep starting over, not really having a solid enough idea to bang out 20 pages for. That goal at least seems more manageable. Considering what I spent for the camera, I better get my shit together.
I think I know what it is that causes this lack of concentration, and it's a mix of things that I mostly can't control that keep me too frozen to concentrate on anything aside from sleeping. It's no fun at all. I think the plan of action is to resolve or accept the issues, and make a plan to complete the things I want to do, with deadlines. Every software project I've ever been on has a plan, so it makes sense to have one for my own.
You sound like you just need to rediscover what gets you back into that coding "zone." A little bit of alcohol and techno/trance always worked for me when I needed to hunker down and pump out some major coding.