大家看看我这代码有什么问题啊?

为什么我只有第一条信息好用 
再输入第2条的时候就没有反映呢?<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>在线报价</title>
<link href="css/css1.css" rel="stylesheet" type="text/css" />
<style type="text/css">
.STYLE5 {
font-size: 12px;
font-family: "宋体";
color: #FFFFFF;
}
</style>
</head>
<body>
<div id="header">
<div id="logo">
            <div id="ymsm">在线报价</div>
        </div>
    </div>
    <div id="center">
     <div id="centerz">
      <img src="images/zxbj_04.gif" width="144" height="476" /></div>
        <div id="centerc">
<table width="690" border="0" align="center" cellpadding="0" cellspacing="0"><tr>
<td height="75" valign="top"><img src="images/zxbj_05.gif" width="690" height="70" /></td>
</tr></table>
<?php
include_once('./config/db.php');
$db=mysql_connect($dbhost,$dbuser,$dbpass) or die('Unable to connect');
mysql_select_db($dbname,$db) or die(mysql_error($db));
mysql_query("set names 'utf8'");
$sqlbj="select * from jh_aproject";
$resultbj=mysql_query($sqlbj,$db) or die(mysql_error($db));
while($rowbj=mysql_fetch_array($resultbj))
{?>
<table width="100%" border="0" cellspacing="0" cellpadding="0" id="tb1">
<tr><td width="18%"><span class="STYLE5"><? echo $rowbj[aproject_name];?></span></td>
<td width="18%"><span class="STYLE5"><input type="text" size="6" value="0">
<? echo $rowbj[aproject_units];?></span></td>
<td width='20%'><span class="STYLE5"><input type="text" size="4" 
value="<? echo $rowbj[aproject_value];?>" readonly="true">元</span></td>
<td width="20%"><span class="STYLE5"><input type="text" readonly="true"></span></td>
<td width="24%"><span class="STYLE5"><? echo $rowbj[aproject_about]; ?></span></td></tr>
<? 
}
?>
<tr><td></td><td></td><td><span class="STYLE5"><div id="total"></div></span></td><td></td><td></td></tr>           
</table>      </div>
        <div id="centery">
        <img src="images/zxbj_06.gif" width="169" height="476" />
        </div>    
    </div>
    <div id="footer">
        <div id="wz">
        </div>
    </div>
</body>
<script type="text/javascript">
var tb=document.getElementById("tb1");
for(var i=0;i<tb.rows.length;i++) {//如果有标题就从1开始
    tb.rows[i].cells[1].getElementsByTagName("input")[0].onkeyup=function() {
        var total=0;
        for(var j=0;j<tb.rows.length;j++) {
            var row=tb.rows[j];
            var val1=row.cells[1].getElementsByTagName("input")[0].value-0;
            var val2=row.cells[2].getElementsByTagName("input")[0].value-0;
            if(!isNaN(val1) && ! isNaN(val2)) {
                var v=val1*val2;
                row.cells[3].getElementsByTagName("input")[0].value=v;
                total+=v;
            }
        }
        document.getElementById("total").innerHTML="总价:"+total.toFixed(2);
    }
}
</script>
</html>