Some possibilities (some are repeats of above posts):
1) You were mistaken that she had a crush on you.
2) She doesn't remember you.
3) She had a crush on you, and remembers you, but you ignoring her hurt her/made her mad enough that she wants you to feel some hurt.
4) She was so hurt back then that she wants to forget the hurt.
5) She is too busy to respond.
6) She is in a relationship.
7) She liked you then but you would not be her current "type" and she doesn't want to encourage you by responding.
8 ) She is a nutjob that you are better off not being involved with.
I'm not that familiar w/myspace, but is it possible she didn't receive your message? If that is not a possibility, I wouldn't contact her again. As others have stated, it's time to move on. Do not let this occupy your brain so much. There are literally approximately 3 billion other girls out there. You did the right thing by apologizing....now it's up to her. Sorry you're having a bad time right now
but it will pass! 
1.) after all the things I listed how could I be mistaken? who does those things to somebody they don't like?
2.) how do you completely forget someone 3 years later when they clearly knew you existed?
3.) that's a possibility I think
4.) that's a possibility I think, remember the last time we saw each other she was staring at me looking pretty sad
5.) she logs in every day and nobody is too busy to type out a simple paragraph
6.) it says single in her profile and she's updated 3 times since I found her page
7.) I guess that's a possibility but how do you go from acting like somebody is your exact type to not liking them at all? See made me feel like I was Brad Pitt the way she looked at me. I've leaned out somewhat since she last saw me and everybody says I look better. Unless she has a thing for chubby cheeks I don't know, i can't imagine anybody thinking I looked better then.
8.) I think she may be a nutjob. Remember I said it seemed she was trying to make me jealous. It's kind of stange how she walks right by me with another guy and she says to him "you're sexy" what a coincidence

and she didn't just say it she practically shouted it, also i would think a normal person would reply with some sort of response after somebody says nice things about you. If some girl I thought was completely unattractive said the same to me on myspace I would atleast thank them and try to find something nice to say about them.
I actually don't use myspace often either but I created another profile just to send my message to see if it worked and it did work. The message i sent her is also in my "sent item" folder. I know I should move on but it's easier said than done. She honestly was one of the most physically attractive girls i've ever seen and I can't say i've seen many girls as good as her since then. I haven't had much luck with the ladies since then and not getting a simple response from her is very disappointing and confusing. I just wanted to communicate with her that's all, she moved thousands of miles away so I didn't make it out to her like I wanted to get together with her soon.
Thanks for your input