My parents won't admit I'm crazy?

First off, I know enough about myself and mental illnesses to know that I have a tendency towards depression. Ever since I started puberty, there have been entire months where all I could do was fixate upon something self destructive: starving myself, killing myself, hurting myself. Sometimes, however, I feel downright homicidal, though lucky for everyone else, I don't act on this particular impulse. And no one has ever noticed. My parents are either just oblivious or are in denial about it. And now, as I'm being forced to sign the papers to go to a boarding school I never liked, they refuse to even discuss the possibility that I might have psychological issues. This is partly because of my mother's position as chief medical officer at a psychiatric institution and partly because of her recent diagnosis with severe adjustment disorder and her family history with mental illness. And though I have talked to my father about it, and he offered to take me to counseling, he never went through with it. I know that given enough stress, I sometimes have nervous breakdowns. What do I need to do to get some help?