If you can't be creative, try being derivative.

Think of your favorite stories, in any medium, and change one thing about them. Then write something--a paragraph, a page, a short story, anything--about what that story would be like with that change.

What if Harry Potter were Draco's brother?

What if Sam had carried the ring to Mordor?

What if Luke Skywalker had been born blind?

This is helpful because most of the material is already there for you--all you have to do is think about the implications of your small change. Doing so will warm up your creative "muscles" in a way that might help you get back to writing.

This is all just for practice, of course. Trying to publish derivative work is a bad idea for all sorts of reasons.