I'm gonna be slightly snarky, but entirely based on my observations, I think your problem is that he's 14. It happened to both my brothers. (Well, one is still there.)
So… good luck with that.
Seriously, though. If he won't play, or give you any idea of what might be interesting to him, or what his goals are, I'd talk to the parents, and tell them to get someone else to babysit for them. I can't stand people who won't be engaged. Life is too cool to be too cool for life.