Help for a really shy guy?

Well, I have had a rough love life.I'm 21 years old and I've never had a girlfriend due to some bad experiences back in high school. Back then I really liked this girl but I was really nervous about asking her out. One day I summoned the courage to ask her out and she pretty much rejected me in the worst possible way imaginable. She pretty much told me she would never go out with me because I was a nerd and a loser (ok, I'm a little nerdy but I'm no loser). She even went out of her way to start telling other people that I was a creep and a loser. There was another girl that I liked back in high school. I told her I liked her and she told me she did too and we even made out but she then ran off with another guy.Now if I like a girl I am completely horrified to ask her out. So much that I just don't bother trying because I feel I don't have a chance. I can ure you I'm funny, quick witted, smart, honest, good natured, goal oriented and actually not bad looking but girls don't seem to notice me. Perhaps me being too nice is what is holding me back. Anyone have any advice for me?