noob: node.js writeHead stopping my code

Ok, I'm new to Node.js so excuse the noob question. Heres my simple code:

var http = require('http');
var fs = require('fs');

// simple node.js server

server = http.createServer(function (request, response){

var get_text = function (errors, contents){
    response.write(contents);
    response.end('hello world');
}
// get_text is the callback
fs.readFile('log.txt', get_text);
response.write('End of the callback');

response.writeHead(200);
});

server.listen(8000);

console.log('Server running at port 8000');

As it stands, when I run the script in my terminal it will start the server properly but when I go to my localhost:8000 in my browser (chrome) it comes up as "webpage not available".

If I comment out the writeHead command it works fine.

Why?