How can I get a guy to stop and talk to me?

start a new conversation after hello...
ask what are his classes... what he study or sumthn like dat...carry on da conversation til you two get comfortable tlking to each other...

Well he might be in a hurry to get to class, so I'd think twice about having a long conversation with him. I know when I say hey to people in the halls and they're going to other way I can't get much in. Perhaps you could try using the little time you can get to say something like "Hey (name), we don't get to talk anymore! we should hang out sometime!" and give him your number or ask when he's free to hang out. Alternatively, if you don't want to jump straight to hanging out, ask him if he's in a hurry before you talk and if he isn't ask him if there's a free period he has where you two can chat. Of course, like thegodfather said, change up your appearence, hair, makeup, clothes, whatever and carry yourself with confidence. If you make a nice impression on him he'll definately want to see you again.

wear something different
do you hair differently

look pretty act pretty, try again.

If he's one of those people who get to class as fast as possible, there probably is not time to talk. Look around for him before and after class, you might see him one day. Not to stalk him or anything, but hey you're bound to find him somewhere. Try to get his number ;D