index.ph on url problem.

[eluser]ryanermita[/eluser]
i having a problem with the index.php on my url. when i removed it, it gives me an error of:

"Object not found!
The requested URL was not found on this server. If you entered the URL manually please check your spelling and try again.
If you think this is a server error, please contact the webmaster.
Error 404
localhost
Apache/2.4.3 (Win32) OpenSSL/1.0.1c PHP/5.4.7"

the code inside the .htaccess file located inside the application folder:
RewriteEngine On
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php/$1 [L]

together using this htaccess i remove the index.php inside the config.php "$config['index_page']"

and when i return the index.php. the connection of my css when reload using different function is not working. on homepage the css is working but when i test my code and reload again the login page the css is not working.
heres my controller function:
<?php
Class Administrator extends CI_Controller{
function index(){
$this->load->view('administrator_view');
}
function validate_credentials(){
$this->load->model('administrator_model');
$query = $this->administrator_model->validate();
if($query){
$data = array(
'username' => $this->input->post('username'),
'is_logged_in' => true
);
$this->session->set_userdata($data);
redirect('dashboard/home');
}
else{
$this->index();
}
}
}
?>


thank you, im just a beginner using this framework. and sorry for my bad english