how can I get a girl interested me who isn't interested in me? ?

If she doesn't have any initial interest, you won't be able to raise her interest. If she starts out with a 5 interest level, you can raise it to an 8 easily, but if you're starting from a 0, what's it gonna do raising it to a 3? You're wasting your time. 

It does help to be a drummer. Learn to play the drums. Or learn to skateboard or surf. Or learn to fly a plane. I know a guy who learned to fly a plane to impress a girl and ended up really liking flying the plane! In other words, start learning to do something useful, like learn a language, learn to cook really good, or learn to fish. By having successfully completed an action, you now how something of interest to talk about. I mean, just knowing about trees and how to grow a forest could keep me occupied for hours. Get a dog and take it with you everywhere, get a pickup truck and go fishing - the people who have something of interest to say are the ones who do something other than sit around. Good luck to you, but, learn to do something fun and different and stand out from the crowd.

You can't. If she isn't interested, she isn't interested.