When I have writers block, I just start typing with no intent on actually writing the paper. I generally start with typing this - "blah blah blah, I can't think about anything to write about the intersection of morality, philosophy, and psychology. Hmm.. a bunch of famous people would have ideas though.. Kant would say..."
anyways, I continue like that until I have about 1/2 a page and then usually a thesis will poke its head out of the crap. Once the page has text on it, you aren't so intimidated by that blank page. Just make sure not to turn in a paper that starts out with "blah blah blah." (I actually made this mistake once by printing the wrong version of a paper.. oops!)