I need help with a problem with a girl I like?

Okay so there's this girl that I really like. For some reason, I can't muster up the strength to talk to her or anything. I've asked her out like a year ago but she said she likes me as a friend.But recently one of her friends tells me I might have a chance with her because sometimes she asks about me and even one time she got on Facebook just to tell me Happy Birthday and felt bad because she didn't tell me earlier (She hasn't gotten on in 4 months before that). She also says Hi to me and smiles at me every time I see her in the hallway or even stares at me sometimes. Should I ask her out again? Do you guys think she's interested in me also maybe? And how can I talk to her more without being so damn afraid?