Giving up...?

A person close to me has been struggling with feelings of depression for quite a while. It seems sometimes like he has given up on life in general. He gets a lot of crap because of his disablity, especially since it is one that can't be seen. Simple things to most are difficult for him and when people get angry with him for "screwing" things up it really hurts. I even catch myself getting angry when I know I shouldnt. It makes me feel awful when I don't know how to help. I know since I'm not living with it I can't begin to understand but I still want to do something. How do you let someone know that you haven't given up when they have given up on everything?