I Have a Question

Okay, so I've been on a couple of dating sites, one for a few months and the other for just a few days now. I've sent lots of different kinds of messages to many different women, and still nobody (as in 0) has replied to me. It's not like I'm asking them to marry me; hell, I'm not even asking them to go out with me! I'm just trying to start some conversation, and I might as well be talking to the wall. Nobody will give me the time of day. Is there some kind of secret to getting people to reply to your messages?