Lack of motivation/depression help?

For the first time I've failed all of my major classes. I'm an AP student, I scored pretty well on my PSAT and so far I've passed all the required regents, but lately I don't see the point. I don't care about grades like I used to. I can't pay attention in class because I'm always in deep thought about something else. Everyone tells me about college as if to motivate me, but honestly I have no college (or life) plans. As a kid I wanted to be an Author, and then a comic book Artist, and then I wanted to be a professional Bassist and start my own Bass program. I don't really believe I can do "anything I want to" anymore, because honestly, I don't think I'm good enough for anything, and I feel like I'm wasting my time, preparing for a future that, in my opinion, isn't so bright. Lately I've felt pretty low, I keep having suicidal thoughts, because I don't think I'm ever going to be a success.