mysql not working with php

Question

 I'm using Apache2, php5, and MySQL. Every time I try to run any database action in PHP, all scripts stop.

In the php.ini, I did enable the following :

extension=php_mysql.dll
extension=php_mysqli.dll    

The code to test the database:

echo '<p>testinp php script</p>'; 


// mysqli
$mysqli = new mysqli("localhost", "root", $pw, $db);

echo 'Still here<br>';

$result = $mysqli->query("SELECT * from test");
$row = $result->fetch_assoc();
print_r ($row);


echo 'Still here'; 

The "Still here" message is not displayed. How can I fix this?