What's wrong with my toe nail?

It's on my big toe on my left foot. It's pink on the bottom half like it should be, but on the top, it has a white-yellowish tint. I think it might not even be connected to my toe; i think it's come off! There's also black dots under the nail, and i think it's dirt that somehow got in really deep. Is this normal? Can I fix it? Will I have to half the nail remove? I do have a bunion on that foot, if that can help explain anything.