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His school work is a number one priority. He is 17 and is choosing the silent treatment as a way to get back at you. At this age, he should understand what you are trying to do- help him.
If he had stopped going to his classes mainly because of the game involvement, then you've done well to consequent and take the game away. If you believe that he had stopped going for other reasons and the game was a way to distract himself, you would need to address that.
In order for him to earn the games back or any other privileges for which you provide, he has to show some changes in his behavior. You may decide what would constitute earning these items back and let him know what will lead to being taken away again.
He could have developed an addictive behavior and that needs to be addressed. He is 17 and still under your roof but his behavior from what you've shared is immature.