Whatt's going on?!!!?

Okay here’s the deal. There’s this girl in one of my classes (college). I kind of knew her in high school but never really talked to her on a regular bases. Anyway, on the first day of class, she was really friendly and flirty (she’d poke me in the stomach, talk a lot, smile frequently at me, seek me out as her partner for exercises) and at the end of class, I had gone ahead and was at a considerable distance from our building and yet, she made an effort to catch up to me and we ended up talking all the way to her car. Now I’m not saying that I’m head over heels for her but I do find myself starting to like her. The only problem is that recently, she hasn’t been talking to me unless I initiate the conversations–it’s like she’s mad at me and giving me the silent treatment. What HAPPENED!!?! I’m completely stumped as to how to approach the situation (does she like me or was she just being friendly?) and the bad part is I can feel this thing turning into a full blown crush (which I hoped wouldn’t have happened until I got to know her better). Please help me analyze the situation and help me shed some light on what her deal is. Should I try to get closer to her regardless or just forget about her all together?