change the hidden field to a text field so you can see what it;s value is before submitting the form:
<input name="hiddenField" type="text" id="hiddenField" value="<?php echo $row_ntu['ntu_date']; ?>" />
also, I don't see a submit button the form. your form needs to have a submit button in it in order to submit the form. with out a submit button, the form is not being submitted.