Change locations.
Open up a new document and write in that.
Try writing longhand on a piece of paper.
Reread what you have and annotate it.
Do a chore you've been putting off.
Brainstorm titles.
Format citations.
Reread part of the text that inspired your thinking.
Send a paragraph to a friend to get their quick take.
Set a timer for 10 minutes and write an impassioned essay about how much you hate writing. Then try again.
Imagine how you would explain an idea from your work to your parents, or to your students, or to an alien new to the planet.
Answer the question: who needs what you are writing?
Writing is hard, and it is easy to wait until you feel inspired to write. But, if you can get in the habit of writing when you say you will, no matter how you feel about it, you can begin to test the hypothesis that you need to be inspired to write. It doesn't have to be pretty. It doesn't have to be new words on the page every time. It doesn't have to go in the final draft. But endeavoring to keep your appointments for writing with yourself is a habit worth building.