为什么点击了老是没反应

<form id="form1" name="form1" method="post" action="">
<div align="center">
<table width="30%" border="0">
<tr>
<td>输入学号</td>
<td><label>
<input name="zhanghao" type="text" id="zhanghao" />
</label></td>
<td><label>
<input name="chazhao" type="submit" id="chazhao" value="开始查找" />
</label></td>
</tr>
<tr>
<td>选择班级</td>
<td><label>
<select name="select">
<option value="a">网络1</option>
<option value="b">网络2</option>
<option value="c">网络3</option>
</select>
</label></td>
<td><label>
<input name="banjichazhao" type="submit" id="banjichazhao" value="开始查找" />
</label></td>
</tr>
<tr>
<td>选择老师</td>
<td><label>
<select name="select2">
</select>
</label></td>
<td><label>
<input type="submit" name="Submit3" value="提交" />
</label></td>
</tr>
</table>
</div>
</form>
<?php
if(@$_POST["banjichazhao"]=='开始查找')
{
if(@$_POST[banji]=='a')
{
$sql="select * from xuantibiao where 班级='网络1'";
$res=mysql_query($sql);
?>
<table align="center" width="80%" border="2">
<tr align="center">
<td align="center" width="40">学号</td>
<td align="center" width="40">班级</td>
<td align="center">课题名称</td>
<td align="center">开发工具</td>
<td align="center">主要功能描述</td>
<td align="center">指导老师</td>
</tr>
<?php
while($row=mysql_fetch_array($res))
{
?>
<td align="center" width="40"><?php echo $row['学号']?></td>
<td align="center" width="40"><?php echo $row['班级']?></td>
<td align="center"><?php echo $row['课题名称']?></td>
<td align="center"><?php echo $row['开发工具']?></td>
<td align="center"><?php echo $row['主要功能描述']?></td>
<td align="center"><?php echo $row['指导老师']?></td>
</tr>
<?php
}
}
}
?>
</table>
代码查了好多遍都看不出错，点击查找什么反应都没，连传都没传过去