You have the uploaded as test.php, but the forms action is set to post to index.php.
When i submit the form, i can see that the problem is with validation failing, the address inn the bar is index.php?invalid=true
change the forms action to post to the test.php page.
<form enctype="multipart/form-data" class="Cool_Default" id="Default_Cool_Default" name="Default_Cool_Default" method="post" action="test.php">
I would also like to test that your server is properly configured for sessions.
Please upload the sessionTest.php file from the following post and post a link: