My first impression upon hearing or reading a sentence like this would be that the "not" would be part of the infinitive - but there are better ways of structuring the sentence grammatically that would avoid this problem. Altogether, this sentence wouldn't sound like natural English in its present state. 1) If you wanted the "not" to be part of the infinitive, it would be better to say "I do not want you to play games" or "I would like for you to not play games" 2) If you wanted the "not" to be part of the verb "to be," you could say "Playing games is not what I want you to do" Hope this makes sense! Good luck :)

Jon's answer is good. I'd add one more thing. Often, the words,"not play games" go together without any "to". So "not play games" acts like the object of the verb "is". What I want you to do is not play games, so the compound subject "what I want you to do" is ( equal to) "not play games."