Unable to connect to database server!!!!

Unable to connect to database server
This either means that the username and password information in your settings.php file is incorrect or we can't contact the MySQL database server. This could mean your hosting provider's database server is down.

The MySQL error was: .

Currently, the username is dpusr and the database server is localhost.

Are you sure you have the correct username and password?
Are you sure that you have typed the correct hostname?
Are you sure that the database server is running?
For more help, see the Installation and upgrading handbook. If you are unsure what these terms mean you should probably contact your hosting provider.

今天裝了一天，也看了一天這個畫面了T_T
先簡述我裝的步驟
1. tar zxvf 然後改目錄名稱
2. 進去設定 default/settings.php
3. $db_url = 'mysql://dpusr:密碼@localhost/dpdatabase';
$db_prefix = '';
$base_url = 也有改出來了 其他沒動
4. mysql -u mysqluser -p databasename < database.4.0.mysql
5. files目錄也有建立了

可是還是出現 Unable to connect to database server ...
裝 4.5 很正常, 裝 4.6 後面幾個版本的就開始會出現這種狀況, 4.7以上的一樣...
拜託, 我是不是什麼地方沒設定好阿? -.-?
我的密碼也沒有特殊符號阿.... 怪......

我的MySQL是4.0的