<p>Could be depression, an addiction (including to video games). </p>
<p>What I suggest that your parents do is tell him that he can continue to live at home only if he gets a thorough medical evaluation -- including a drug screen -- and if the medical evaluation shows nothing, also gets into regular therapy with a licensed psychologist or social worker.</p>
<p>Unless he has some serious mental health or health problem that would prevent his working, your parents also could tell him that he can continue to stay at home only if he gets a fulltime job -- and pays a reasonable amount of rent. If he's working on his GED, he can do that while working fulltime. That's the real world: People without GEDs have to work to support themselves, and typically, they aren't able to afford the kind of comfortable surroundings that presumably your brother is enjoying at home even if your home happens to be modest.</p>