Your son seems distracted and doesn't care about school. You are also having difficulties talking to him. Briefly, if you are concerned about the change in his behavior, consult with the teacher and school counselor. Let them know what you have observed at home. Make a list of your conerns before the conference.They may be able to give you some insight about his academic performance, social and emotional status at school, and helpful suggestions.
If you discover the problems are serious, you may want to explore counseling outside of the school. This will help your son to express his feelings and build on his strengths.