My dad won't stop talking to himself, what should I do?

I'm the youngest of three boys in my family and my father is a stay at home dad who renovates our house by himself and does all the work of a homemaker. My brothers are both off at college during the school year, and my mom travels on business frequently, leaving me alone with my dad a lot. He has been talking to himself for 4 years now constantly, with no sign of getting better. Even when I'm with him he doesn't even try to stop himself, and when he isn't talking to himself, he is gazing off in the distance and laughing to himself. Whenever I tell him something he has no capacity to remember it, and he has absolutely no interest or involvement in my day to day life. I spend my days either away from the house or avoiding him after learning the hard way just how awful it is to be near him. He never leaves the house and doesn't really have many friends outside of his college friends that we see once every couple of months, and refuses to try to get more friends, or become involved in anything, and won't be social at all. I have no idea what more I can do after reminding him constantly to stop, telling him when he's being weird, and suggesting he find some sort of hobby or social life. What more can I do? Please help.