I kept having that problem, it turned out the server didnt have PDO enabled. To find that out make a new .php in public_html, and stick the following code in it. Go to the page and it should say 'PDO available' at the top, and anything besides '--enable-PDO' ' in the box of commands... I wanted to make sure so I put two PDO detecting codes on that page. :P Its also handy for checking out whats installed on your server. If you dont have PDO enabled you'll have to request it from your server host, its fairly easy to do I think. And you wont be able to get much further without it, sorry. :( If you want any help I'll be about all night.
Code:
<?
if (!defined('PDO::ATTR_DRIVER_NAME')) {
echo 'PDO unavailable';
}
elseif (defined('PDO::ATTR_DRIVER_NAME')) {
echo 'PDO available';
}
phpinfo();
?>