Dude. This has been going on for awhile now. I think it is time to ask. With, my now wife, Chloe, i waited two years to pop the question because i was too shy. And then i found out that she always wanted to be with me so when i went out with all these other girls she thought i was not interested. Look, get her on MSN or sumin and ask. If she says no ask her if we can still be friends. If she says no again then i am geussing she is not the one you are looking for. Really, girls, if they say no to a relationship and to being friends, they don't want you. However if they are willing to be friends then thats brilliant. And with the ignoring one day and the talking the other, it seems to me she is just shy when you are attracting her, and not so shy when you aren't so she just likes your personality to talk to you.
It won't hurt in trying man. Believe me, if you think a girl digs you, don't wait to long to ask her out or she might think you are not intrested and go looking else where. Now that, that would be shit. Good luck man.