Start by doing some debugging. If the file that is not doing anything is expecting $POST or $GET data from the preceding page, add the following at the top of the receiving page to see what was actually received:
<?php
echo "<pre>";
print_r($_POST); // or print_r($_GET) if applicable
echo "</pre>\n";
Make sure you're getting all the error outputs that PHP has to give you:
<?php
ini_set("display_errors", 1);
error_reporting(E_ALL);
Check return values of things like mysql_query() calls and use die() or user_error() with some useful information if it fails. For instance:
$result = mysql_query($sql);
if($result === FALSE)
{
user_error("Query failed: $sql - " . mysql_error(), E_USER_WARNING);
}
