In order to for your questions to be randomized, you must import them from the Question Library into a random section folder in the quiz.
If there are already copies of your questions in the Question Library, you can delete them from your quiz and then import them from the Question Library to a random section folder in your quiz.
If there are no copies of your questions in the Question Library, you can import your questions into the Question Library from your quiz. Once your questions are in the Question Library, you can delete them from your quiz and then go to your quiz and import them to a random section folder.
For instructions on importing questions to a random section folder, see the Online Help section Randomizing Question / Selection Order.