One sentiment common among all OTD kids (really most teenagers in general) is that the most they are reminded of something that others, but not they themselves, think they should be doing, the more they won’t want to do it. Even if he might consider davening, the more it becomes a fight, the less interest he will have. He knows G-d thinks he should do it, but the more he feels your respect of him is dependent on his personal ben adam lamakom, the more he feels like you’re jutting into his privacy.
I don’t mind sharing how I found my way back but I’m not sure how it would help. You mentioned he believes in G-d – I didn’t, nor did i believe in the validity of the Torah. Doesn’t seem like he and I were dealing with the same situation. Except what I said about proving that the Torah is awesome. Don’t try to be in competition with video games. Just however much pleasure you get out of keeping the mitzvot, work on yourself to love it more and the enjoyment will be infectious.