Writing Fearlessly

I have a problem. I cant do it. I know what I want to say, I can see the sentence formed clearly in my mind. The emotion of my characters, the pain that needs to be portrayed.
It's a pivotal moment. The moment when the characters reach a new level of understanding, their relationship progresses. It's terrifying and painful.
And yet here I am. My fingers gently tapping the keys feeling them, but nothing is being written. No letters string together to form words.
The scene plays in my head over and over and the fingers refuse to obey and write.
This is the part where I growl at my computer. It's my computers fault. It wont listen to me. Bastard.
But the bastard is really me. I am stopping the words from being written.
Why is it in my day to day life I open my mouth and the truth comes out fearlessly. I sit down to write and my fingers freeze.
Am I thinking about my audience too much? The thought of them is poised in the back of my head and when I get down to the grit and grime of my story the evil audience rears it's ugly head.
Am I afraid of what the people I know will think of me when they read what I have written? Yes. That was easy.
Now here's the funny part. The zombie comedy that I am writing as an outlet for the one that is yet to be titled, I have no problem sharing. It's crude, and perverse. It's blunt and rubs certain issues in people faces. I have no qualms about sharing that one.
In fact I tell people I cant wait for them to read it and have sent pieces to friends.
But untitled? Nope. Only two people know the story. Two that I trust. I have giving my husband an over view, but its not really his thing and I wasn't expecting much when I told him. He's supportive, but he's about as interested in a love story as I am.
How do I unblock myself? How do I write what I want? Why is it I cant do it?
How do I write fearlessly?