I'm 16, doing quite poorly in school, and I simply can't see the importance of it all. What do I do?

I'm 16 years old. I'm a junion in high school. Things have been downhill since I was expelled Freshman year, and suspended sophmore year. I've completely given up on school. Not even by my own will, the motivation simply isn't there. College is closing in faster and faster. I simply cannot get myself to see the importance of it all. It's as if my brain has completely given up on myself. What can I do to fix this?