เวลากดปุ่ม แล้วไม่ยอมเปลี่ยนหน้า พอเอา table id=styletable ออกก็สามารถใช้งานได้ตามปกติ

<style type="text/css">
#colortext{
color:#666666;
}
#styletable
{
	font-family: "Lucida Sans Unicode", "Lucida Grande", Sans-Serif;
	font-size: 12px;
	background: #fff;
	margin: 0px;
	width: 472px;
	border-collapse: collapse;
	text-align: left;
}
#styletable th
{
	font-size: 14px;
	font-weight: normal;
	color: #093;

	border-bottom: 2px solid #093;
}
#styletable td
{
	border-bottom: 1px solid #ccc;
	color: #666;

}
#styletable tbody tr:hover td
{
	background: #cf9;
	color: #000;
}
</style>


<?
$r=$_GET["r"];
$conhost=mysql_connect('localhost','root','1234');
mysql_query("Use project;");
mysql_query("SET NAMES UTF8");
if($r==1)
{
	        echo "<table id=\"styletable\">";                            <------------------------------เอาออกใช้งานได้ปกติ
		echo "<tbody>";                                                     <------------------------------เอาออกใช้งานได้ปกติ
		echo "<tr>";
		echo "<th style=\"width:50px; text-align:center;\"><center>รหัสวิชา</center></th>";
		echo "<th><center>ชื่อวิชา</center></th>";
		echo "<th style=\"width:50px; text-align:center;\">หน่วยกิต</th>";
		echo "<th style=\"width:30px; text-align:center;\">ปี</center></th>";
		echo "<th style=\"width:30px; text-align:center;\">เทอม</th>";
		echo "<th style=\"width:30px; text-align:center;\">เพิ่ม</th>";
		echo "</tr>";
		echo "<tbody>";
$result=mysql_query("select * from subject");
while($dbarr=mysql_fetch_array($result))
{
		 echo "<tr>";
                 echo "<td>$dbarr[coursecode]</td>";
                 echo "<td>$dbarr[titlethai]</td>";
                 echo "<td><center>$dbarr[credit]</center></td>";
		 echo "<td><form method=\"post\" action=\"addsubject.php\">";
		 echo "<select name=\"year\" id=\"year\">";
                 echo "<option value=\"1\">1</option>";
                 echo "<option value=\"2\">2</option>";
                 echo "<option value=\"3\">3</option>";
                 echo "<option value=\"4\">4</option>";
                 echo "</select>";
	         echo "</td>";
	         echo "<td>";
                echo "<select name=\"term\" id=\"term\">";
                echo "<option value=\"1\">ต้น</option>";
                echo "<option value=\"2\">ปลาย</option>";
                echo "<option value=\"3\">ซัมเมอร์</option>";
                echo "</select>";
	        echo "</td>";
                echo "<td><input type=\"submit\" name=\"submit\" value=\"เพิ่ม\" onclick=" ?>"return confirm('ได้เพิ่มข้อมูลลงฐานข้อมูลแล้ว')" /><? "/>";
		 echo "</form></td>";
                echo "</tr>";
}
                echo "</tbody>";
                echo "</table>";
?>