What should I make my son do this summer when he is failing school?

My seventh grader has had a miserable year in school. Academically, he could not have given less to his homework and studying. Last year he was in the top five percent of his cl. He rec'd awards for his grades, he is in the gifted program and takes advanced math. I don't know why, but this year he refuses to do homework, I don't think he has opened a text book and refuses to bring them home. He refuses to study. He has pulled a 70 average through out the year. I try to help him every night, I organize his papers and stand over him to make him do his homework. Now that it is at the end of the year he is jeopardy of failing. He is obsessed with Ruin scape (an online game) and you tube, which I have banned him from both. Usually in the summer he goes to a great camp but this year I haven't enrolled him. I have threatened to make him go to work with his father everyday and work in a warehouse. What can I do to make him take it all seriously? He doesn't seem to get that he is on a downward spiral?