What do i do about this girl?

Theres this beautiful girl that im friends with,.. shes really preppy and im just more of a punk but im clean cut and respectful.. yet i wear skinny jeans and oversized t shirts. its not as bad as it sounds. anyways i really like her and i talk to her alot but i cant tell if she is interested,, shes sad the past few days and wont tell me why and its all really confusing.. how do i tell if she likes me! i just dont feel like i could ever get a girl like that..