Alright, you need to know a few things about women's experience on POF.
Every day they'll log on and have a dozen or more messages. 90% of them are one of the following.
Or one of the following - a lengthy essay about the guy's life story, a canned pickup line, or some needy awkward essay begging her for attention.
Your messages so far.
First one - indisinguishable for every other guy, shows no creativity. Unless you're absolutely gorgeous or something, she's just going to be annoyed by you because you're not even making an effort to show her any personality.
Second one - You go in talking about yourself, topics that are completely irrelevant to her and she has no reason to care about them. You gave no indication you even read her profile.
Third one - Your best effort, but still not very good. You open with "sweetheart," which is way too intimate a label for a woman you haven't even met, and it suggests you're trying to manipulate her. You said you liked the profile and pictures but once again didn't show any evidence that you actually looked at them.
Put aside your indignation and try to see it from their perspective. If you were receiving 2 dozen messages per day, what kinds of messages would stand out to you? What would you want to receive?
"Hey, your skydiving picture's totally badass. I'm jealous. I want to do it so bad.
Saw you like Harry Potter. And you have a pet snake. You a slytherin?"
You don't have to be that clever. You just need to be a little clever, and not an echo of every other man who messages her.