Note: And no, this is not my friend Steve, or my friends Son Steve. :)
You've hit a dead end. You wrack your brain figuring out how the heck you've gotten to this suddenly insurmountable barrier; one that not even Superman could leap, or Spidey climb!
Now you're stuck, and feeling trapped, you are in almost physical pain, and you cannot see a way out.
You can either see it two ways; as a positive or as a negative. Pessimistically "Oh woe is me! I'll never be able to write again!" Or as a positive, "Why am I blocked? What are the muses/writing God's/esses trying to tell me?"
Sometimes that is all writers block is. What am I supposed to be looking at? What am I supposed to be learning? Or is this just my brain telling me to take a break? Usually it is the last thing when I get it. And yes, I do get it.
Ways of getting through that wall, or taking it down rather.
I. Making Friends with Your Block.
Asking it what it wants? Call it Steve if you want ("Over the Hedge" Reference BTW).
Seriously, ask it why it is there? Ask for the reason it has chosen to spring up at this time? My blocks are usually a sign my mind is rebelling. It's having a temper tantrum of Katie Kaboom proportions (cartoon reference)
I'm ADD as well, so I have a very short attention-Squirrel-Oh where was I? Ok-shiny-oh right, SPAN. Which makes my brain even more unruly sometimes.
I have a hard time making a set schedule, or even deadlines (which adds to the writers block, and I love to wave at them while they pass by). ahem.
Which leads to...
II. Writing Warm Ups.
Writing is an exercise, and much like running, requires stretching the correct muscles. A good way to even stop a block from even forming in the first place, is writing practices, consult Natalie Goldberg's "Writing Down the Bone," for more info. Ten minute writing sprints in which you just keep your pen moving across the page without censoring, or editing. Going with first thoughts, going for the jugular. Taking no prisoners!
Doing a couple of these before you start your "Real Writing," can help your mind focus better, and I find my writing flows better.
Handwriting your practices is also good as it uses a different part of the brain. Also I recommend using a notebook, cheapo spirals are good. Once you have filled one, re-read what you have written in practice, highlighting what you liked, what was most powerful. These can be whole paragraphs, sentences, or even words. These can become prompts or ideas for future projects. You can also move these to a catalog (I suggest a spreadsheet) which has references to where they came from, i.e. May 2010 notebook, date, and which prompt it is from.
If you choose to go route 1, then I recommend "Writing from the Inside Out! Transforming your Psychological Blocks to Release the Writer Within," by Dennis Palumbo, MA, MFT, C 2000 by Wiley & Sons. Dennis Calumbo wrote screenplays for "My Favorite Year," and numerous other TV shows and pilots; as well as the novel, "City Wars." What is great about this is he works with creative people/writers.
If you go with 2, than either Natalie Goldberg's, "Writing Down the Bones," and "Wild Mind," are excellent. And also "Outwitting Writers Block,' by Jenna Glatzer is also really well done.
Whatever method you choose, good luck, and let me know how you get around/through/over/or under your writers blocks!
Jack Heffron, also has some writing prompt books, and also look at Writers Digests Writing Prompts. There are a ton of prompt books out there, and check your local library for any of the above.