Okay, you've scheduled time for writing, told your spouse you need x number of undisturbed hours, picked your topic, maybe even have an outline, but you're sitting there and....Nothing!
How does one overcome writer's block? Writer's blocks are overcome by writing. I know that sounds ridiculous, because if you could write then you wouldn't have writer's block, now would you? But the truth is that it's not so much that you can't write, it's that you don't know how to start. Or at least, how to start THIS time.
Writer's block can occur at any time during a project, beginning, middle or end. How to deal with it depends on what it is you're trying to write. There are two basic types of writing, fiction and non-fiction, and dealing with them requires two steps. The first step is the same for both, but the second steps are very different.
Let's deal with fiction first, just because it's more fun. In fiction, the problem is setting your imagination free. All kinds of things block up the imagination, most of them having to do with real life. Bills, relationships, car troubles, work stress, all that stuff can distract you, pull you out of the creative process and make it difficult to escape' into the imagined world that you are wanting to create or describe. These two steps always work for me, and I guarantee they'll work for you. I didn't invent these; I learned them from others, but I put them together for this specific purpose.
First step: Breathing. Yes, that's right; Breath! Before you try to write anything, sit at your desk with your back straight,. Set your feet flat on the floor, close your eyes and place your right hand on the top of your head.Take 10 very long slow deep breaths in and out while focusing on the back of your eyelids. Then take your right hand down and put your left hand on top of your head and do another 10 long slow deep breaths. This is bringing you into present time. (Hint, this is good to do even if you don't have writer's block.)
Second step: Keep your eyes closed, put your hands on your keyboard and start typing. Describe the inside of your eyelids, the way your butt feels on the chair, the temperature of the room, any sound that you hear, how your muscles feel. This is all stuff you are going to throw away, so don't worry about spelling, syntax, grammer, flow or any of that, just let it come out.
Keep going until you find yourself back in your imagined world, with your characters and your situation, but still don't force it into any particular scene yet, just keep describing where the people are IN MINUTE DETAIL. Purposefully stay away from having anyone say anything, or do anything other than mundane things. Just keep describing to the point of the ridiculous. Eventually, I promise you, you will find yourself writing the story you want in the way that you want it. The more you use this technique, the faster it will come. At the end of your writing session, go back and find where in that mass of words it started making sense, and delete everything before that point. It was the bridge you used to get across the chasm. The real story is all on this side.
For Non-fiction, there are also two steps, and like I said, the first one is the same as for fiction, so go back and read that.
Start an outline. Put your word processor in OUtline mode and list out as main headers the topics you want to cover, in no particular order. Add sub-topics as they occur to you, just two-three words to use as reminders, add sub-sub-topics. Make sure you skip around in the outline a lot. Put the same sub-topic under more than one main topic if it seems appropriate. Keep adding topics and sub-topics and sub-sub-topics and then a sentence or two about the sub-topics and sub-sub-topics. Maybe a little paragraph here and there. Be sure to jump around in your outline a lot with this, too. Don't try to spend too much time on any one part of it. As soon as it stops flowing, move to a different part and write out a few words there.
If you keep this up, eventually you'll have your whole thing written. You'll just have to go through and straighten it out. Move stuff around to a logical order, delete the extraneous and the repetition and add some transitional sentences, an opening sentence (which tells people what you're going to tell them) and a conclusion (which tells people what you told them) and you'll be done.
This really does work in every case to overcome writer's block. I call it Writing Around the Writer's Block.