[eluser]noslen1[/eluser]
You probably haven't correctly set your database connection located in /config/database.php
Code:
$db['default']['hostname'] = 'localhost'; // or distant DB
$db['default']['username'] = ''; // User able to connect to your db, blank or "root" in local
$db['default']['password'] = ''; // You should know it
$db['default']['database'] = ''; // The name of your DB
$db['default']['dbdriver'] = 'mysql'; // If it's running on mysql
