you have the forms action set incorrectly. change line 403:
<td width="379" bgcolor="#FFFFFF"><form action="<?php echo $_SERVER["../Xbox360/PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>" method="post" name="buy_1_ATC_<?php echo $row_nintendods["Title"]; ?>" id="buy_1_ATC_<?php echo $row_nintendods["Title"]; ?>">
to:
<td width="379" bgcolor="#FFFFFF"><form action="<?php echo $_SERVER["PHP_SELF"]; ?><?php echo (isset($_SERVER["QUERY_STRING"]) && $_SERVER["QUERY_STRING"] != "")?"?".$_SERVER["QUERY_STRING"]:""; ?>" method="post" name="buy_1_ATC_<?php echo $row_nintendods["Title"]; ?>" id="buy_1_ATC_<?php echo $row_nintendods["Title"]; ?>">