Writer's block are the two words that every writer understands, and every writer hates.
I have always thought the best way to deal with writer's block is to continue writing! Either go back through your current work and do some editing, reread and get yourself back into the story, or, track down some great writing prompts and write something different for a while. Put yourself in a different situation, and work different muscles in your brain, so to speak. If you're working on a romance, write an intense, mystery scene. If you are trying to write something in the past, try writing something in the present, or future.
And who knows? Maybe whatever you write in the exercise will excite you enough to return to at a later date! :)