Try for fifteen minutes. Fifteen solid, uncomfortable, stare-at-the-whiteness-and-mumble minutes.
Go take care of yourself for fifteen minutes. Eat, drink water, walk, pat the dog.
Try for another fifteen minutes. Endure the buzzing silence and do not saunter into distractions.
Take a half hour to watch comedy and/or exercise briskly and/or make sweet sex. (Bonus points if you manage all three at the same time, although I am informed that two of them go together really easily.)
Try for one more session of fifteen minutes.
If there are still no words, take the day completely off and do absolutely nothing productive. Lay in the backyard and watch clouds. Eat carrot cake. Allow yourself the painful scary time to do absolutely nothing at all.
Try again tomorrow.