problems, custum wrap (class) around PDO, doesn't work

DB::construct();
$STH = DB::prepare('INSERT INTO users (username, password, email, activationkey) VALUES (?, UNHEX(?), ?, ?)');
var_dump($STH);
$result = $STH->execute(array('test', 'nils', 'test@mail.com', '227a038fe9c81515b514cb152188e95c'));

echo "working? <br />";
if($result == false) echo 'noooo...';

It outputs and doesn't put anything in the database. Works with a similare code with DPO just without my DB class. But I doesn't get any errors. Anyone have an idea what the problem could be?

object(PDOStatement)#2 (1) { ["queryString"]=> string(87) "INSERT INTO 开发者_如何学Pythonusers (username, password, email, activationkey) VALUES (?, UNHEX(?), ?, ?)" }
working? <br /> noooo...

The code seems OK (ofcourse, don't know what you've done under the hood). Doesn't PDO itself generate an error / what does var_dump($STH->errorInfo()); say?