When you need to focus and get some serious writing done, it may be a good idea to ditch your word processor and go with plain text instead. Save all your formatting and spell-checking to do later in one step. I just tried this out on a review article I needed to write and found it much easier to concentrate without all of MS Word's squiggly underlining, autocorrecting, autoformatting, and fancy toolbar buttons begging to be clicked. If you're using windows, Notepad works fine, but try out a tiny free program called Q10. It's a full screen text editor that by default uses easy-on-the-eyes light text on a black background. You can also run it directly from a USB stick. When you're done, just open the .txt file using Word, and from there out save it as .doc. By default it comes enabled with some silly typewriter sound when you type, but it's easy enough to turn that off.
Q10 - Full screen distraction-free text editor