Web page degraded when root path is changed

Hi,
I'm setting a wordpress up with nginx.
Everything's seems ok :
- server is up
- phpinfo() test is ok
- the worpress install routine is showing up
The only trouble is the root statement in the web server conf file.
If I use :

[/etc/nginx/sites-available/wordpress]
server{
root /var/www;
index index.php
server_name myweb.net
...
}
I can reach the service using http://myweb.net/wordpress, now I want wordpress to be designated as the root folder.
Here's the change :

[/etc/nginx/sites-available/wordpress]
enter code here
server{
root /var/www/wordpress;
index index.php
server_name myweb.net
...
}

Broken! The web page http://myweb.net is only displaying basic html data, no pics, no css, ... ugly.
No errors reported in /var/log/nginx/access.log
nginx version: nginx/1.2.1
What's wrong?