After a little bit of struggling I've finally got to the login page, but when I enter admin/admin for user and password, it says "Invalid login."
To make it work I've changed database.php file configuration like this:
$db['default']['pconnect'] = TRUE;
$db['default']['db_debug'] = FALSE;
It's really strange, because $config['default_pwd'] = 'admin';
And also, I've set an encryption key (because it was required by installation), maybe that is causing this problem?
Thanks in advance.