Nginx – Can not change nginx 1.2.5 default website

I just installed nginx version 1.2.5 on a new server and discovered that I can not change the default file for default website.

In /etc/nginx/sites-available/default file I have the following lines:

server {
listen 80 default_server;
    server_name myserver;
    access_log /var/log/nginx/access.log;
    error_log /var/log/nginx/error.log;
    root /var/www/default;
error_page 404 /4044.html;
    location / {
        index index.html index.htm;
    }

}

server {
... server2...
}
server {
... server3...
}

Unfortunately, when I open a page by using server's IP address http://ip_address, instead of file /var/www/default/index.html nginx displays it's default file "Welcome to nginx". In case of 404 error it doesn't display the file /var/www/default/4044.html but it's default "not found"page.

I tried to change:
listen 80 default_server; to listen 80 default;
and
server_name myserver; to server_name servers_ip_address

restarted nginx, but no success. Checked error.log file but nothing wrong. I have nginx installed on 2 more servers but olders versions of nginx. There are no problems like this.

Any ideas? If I cannot change its, does anyone knows wher default pages are located so that I can edit them? Thanks.