Try writing in a different location if you typically have one spot you sit and write.
As others have mentioned, set a timer for 3 minutes and write “flow of conscious” sorta like the brainstorming idea.
Try writing with a different instrument. If you normally type on a computer, try using a pen or a pencil or maybe an old typewriter.
Pat Pattison created what he calls “object writing” and his site I believe is called, “Pat’s Parlor”. He is a professor at Berkley. Pick an object to write about, say pepper, write what comes to mind about that object, about the taste, what it reminds you of, how it makes you feel, the colors of it… you may wind up writing about soup in your mom’s kitchen.
Pick a color and tell how you may perceive it not just visually but with all your senses, what would you imagine it to taste like? What would it feel like if you could touch it? What music would describe it?
Anything to get the creative juices flowing!
As you can probably tell, I am not a serious writer (my punctuation is often a sad case), but my “BG” (best good friend) is, so I picked her brain!
Hope you get the flow going again soon ; )