'Overcoming the Nice Guy Syndrome: How to Stop Being Shy Without Becoming A Jerk' which I found both fascinating and rather helpful unlike many other anxiety and depression resources for dealing with our problems; I highly recommend checking this one out (I found it somewhere i can't remember as a free online audiobook i think)...
I'm glad someone mentioned this because I will have to also give it my backing. This audio book is phenomenal, it really changed my outlook greatly.
The reason is something they touch on in the CDs right away. It's your association to "groups". As a man, you have groups and you have a very strong mindset as to how you think your groups are expecting you to act. Your groups are things like "women", "coworkers", "teachers", "religious group" etc. Just a label you put on certain class of people in your life.
So the major major problem shy people have is they have a group or more that they believe, in their own mind, would think negatively of them if they tried to do anything concerning talking to or dating women. For example, one person's group, let's say "women"... the way he grew up, he thinks all women would find it offensive to be hit on. Or another guy thinks all women should be protected from perverted people and so would never dream of hurting a woman like that. etc etc. Or perhaps your family group taught you that women are to be respected, and you wouldn't want to disrespect them by asking them out or scaring them or whatever.
The key would be to define your groups and what you believe your groups think. Then you have to somehow redefine or confront it if you think it's hindering you.
In this case, I highly recommend reading something like Dr. Phil's "Self Matters" which tackles this problem basically head on.
Get both of these resources right now and use them. They both have their weaknesses but they fill in information nicely. In just a few months my outlook on the world has changed dramatically. I am afraid of women about 80% less now, I'm serious.
Don't order the audio CD for Nice Guys off the author's website, it's like $100. Amazon has copies for $30-$40. They are worth it, trust me. Read my review on amazon for it. It explains in detail the weaknesses and strengths of the CDs.