Sometimes when I've went up to a woman and just simply said 'hi' I've gotten ignored completely. These women would treat me like air. Sometimes I've striked up a short conversation and it went okay, but I never got the sense that these women really wanted anything more so I didn't pursue it.
I don't think cold approaching is good, your chances are nil. Especially if you aren't attractive. Unless a woman looks like she wants you to approach I don't think there is any point in approaching her