登录不运行脚本

<script language="vbscript">
function form1_onsubmit
dim a
a=""
if form1.uid.value="" then
a="请输入用户名"
form1.uid.focus
end if
if a=""
then form1_onsubmit=true
else
form1_onsubmit=false
msgbox(a)
end if
</script>
<script>
function dl()
{
document.form1.action="conn.asp";
document.form1.submit();
}

function xg()
{
document.form1.action="modify.asp";
document.form1.submit();
}

</script>
<td height="25" colspan="2"><label> </label>
            <div align="center">
              <input type="button"  value="登录" onclick="dl();">
              <input type="reset" value="重置" />
              <input type="button" value="修改密码" onclick="xg();">
          </div></td>
这个为什么不执行啊？