It's amazing how many times this question comes in, and I think the confusion has to do with the way the female psyche works.
As I pointed out in my answer to this question, Ok, so I saw this movie "He's not that into you" and it really opened my eyes about a lot of stuff, but now I want to know how do you guys act if you are really into a girl? How can we know?, guys make it very obvious when they like a girl. They practically jump up and down yelling when they like a girl (think of that idiot Tom Cruise)--something to do with a dude's caveman tendencies. Nothing subtle here.
Women, on the other hand, LOVE to play coy, shy, stand offish, bored and indifferent, which makes them believe guys are the same way. Guys are not built this way, if a guy likes you, you will know it. He will show you in a thousand different ways.