Have you upgraded the Magento version in the process? In Magento 1.8, "Form Keys" were introduced as a security measure. Having an old template and a new Magento can cause exactly that: some forms not submitting correctly, you won't get an error message but just return on the form page.
In this case, you can add the following to the PHTML file inside the <form> tags:
<?php echo Mage::getSingleton('core/session')->getFormKey() ?>
Andreas von Studnitz, Trainer, Consultant, Developer and CEO of integer_net, Germany.
