Can you explain what you mean by the grading? Where were you unchecking boxes (screen shots might help if you can). Do you mean you don't want the students to see marks or that they don't actually get any marks?
With reference to your comment about the instructions being complicated, one of the problems is that people use different terms for the same thing so questions like yours are very useful to improve documentation. For example here in the U.K. we can use the term grading and marking interchangeably, and the Moodle documentation needs to be in many languages so it can get quite tricky. In the UK we take an exam, but generally in India people say they give an exam.