How can I attract guys in my class?

I am a graduate student in a big university. I am one of the toppers of my class. But I think I give an impression of being too serious. I don't even know a lot of guys in my class. I am shy to approach anyone myself and I appear to be a bit reserved so guys don't always come to me for just talking. Although I do talk to some guys and they are nice to me. But I want to be friends with more people and increase my chances with guys.

I haven't had any date in the two years I have been in grad school. I am a good looking young woman and am sure my physical appearance is not coming in the way of attracting guys. It all has to do with the fact that I appear to be too focused in my studies (and not in a geeky kind of way, rather in a snobbish kind of way).

What to do?