OK People ! Now it works ! ! I had to reinstall it , so I suppose that something went wrong with the first installation ! Now , I will suggest to my friend (who has the same problem) to do the same . May be it will works for him too ! Anyway , thanks to everybody , and expecially to MarianneR : when I saw that he (she ?) got it working on a Mac , I decided to keep trying ... See you all !