Does he show other signs of depression, appetite change, sleep change, lack of interest, sadness, etc?
He sounds as if he is profoundly depressed, although it is difficult to say with the small amount of information available. I would recommend a thorough physical with blood work to rule out any underlying organic condition like hypothyroid,etc. Assuming all physical reports come back to within normal limits, I would then recommend that he be evaluated by a child psychiatrist for the appropriate course of treatment which may include medication and psychotherapy., Many people do not realize that children can suffer from depression and how devastating it can be. You have good reason to be optimistic that with the appropriate treatment his mood may improve dramatically and he can live a fulfilling enriched life. He is lucky to have a parent who is both observant and concerned and strong family resources are an important part of treatment with children.
I have left a link on childhood depression: http://www.nimh.nih.gov/health/topics/depression/depression-in-children-and-adolescents.shtml
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