“There is always, of course, that terrible three weeks, or a month, which you have to get through when you are trying to get started on a book. There is no agony like it. You sit in a room, biting pencils, looking at a typewriter, walking about, or casting yourself down on a sofa, feeling you want to cry your head off . . . .”
A researcher at the University of Pennsylvania has a nice bit of advice for finding a frame of mind that could help you dig out of the rut.