He's smart but is not living up to his ability in any arena of his life.
This part really bothers me a lot. Kids don't lose total motivation without a good reason. The reason could be developmental, which means it will pass if those around him don't force him into the "loser" role. It could be something more serious. One of my sons had something serious happen to him when he was 7 which resulted in behavior that we took him to counseling for. But we didn't find out what actually happened until he was 18, and he's never directly told us. We found out by accident. Talk about regret! I'm not saying that something bad has happened to your son, but you shouldn't ignore all the possibilities. Examine them and follow up and trust your gut.

Also, don't nag. Boys HATE nagging. Turn your expectations around to expect only positive things. The important thing is to maintain a positive relationship with your child for the long run. Things can get worse; they can piss you off worse and do worse things as they get older, and how you handle this can mean the difference between whether they come to you when they're older, or whether they stay away.

Two of my favorite books: How to Talk so Kids Will Listen...by Faber and Mazlish, and Parent Effectiveness Training by Thomas Gordon. I know you have older kids, so you know it's true. They usually straighten out by the time they're 25! lol. We keep telling ourselves "They're going to be AWESOME 25 year olds!"

Karen