Four fail safe cures:
In approximately two thousand words, explain why you cannot write today. Rinse and repeat. Writer's block should be gone within the week.
(Lawrence Block, "Telling lies for fun and profit").
Read a newspaper. Choose three articles, and invent back stories to each event.
("I defy anybody to make this up!" Sheriff Bear, "No Country for Old Men").
Take a bad book and make it better. Take a good book, and make it great.
(Wm. Shakespeare, and latterly The Beatles). No plagiarism please!
When all else fails, drop an alligator through the transom.
(Apologies to Jack Bickham, "38 Most Common Writing Mistakes in Fiction" – what Mr Bickham actually said, was "Don't drop alligators through the transom.")