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I'm always afraid that even if I try, it wouldn't make a difference, and that's where I'm stuck.
I just get this huge..cold jolt of nervousness in my chest
This is where the majority of guys get stuck and never get out of it. They end up living a life they may not have truly wanted with some girl who happened to smile at them one day.
Props for you for analyzing your situation, stepping outside of yourself and recognizing where you are at the moment.
You're on information overload right now: Your brain is swimming in tactics you've seen that contradict themselves. I have been there in the past - finally I just reached down and started gaming.
The first prerequisite is fully believing that you have SO much to offer any girl and that it is an honor for them to even be in your presence, let alone you talking to them.
You said you've opened but it hasn't led anywhere. Start small. Your confidence can be built in the field. Tell the neighbor you like his car. Help an old lady open a door. Ask a hot girl what time it is. It's important to get out of your head, into the field and to take actions, however small. Eventually one day you have the courage to make an offhand remark to a cute girl and just relaxingly see where the convo leads, with no expectations on yourself. You're just out for a laugh.