Yes, you can get a fresh copy as described here, which is also linked from the DLS FAQ Thread. If that is new to you, the FAQ is worth a look to see what else is covered there.
Note that you don’t really know if the tests pass in the notebook, because it did not complete, right? So it’s possible that there is a bug in your code, e.g. an infinite loop. But another possibility is that the server you are assigned to is overloaded. You could try logging out of Coursera and back in again and then trying everything again. No guarantee that will help, of course, but it’s an easy experiment to try.