奇怪的的有关问题，前台的input，type为button，调用后台事件没有反应

奇怪的的问题，前台的input，type为button，调用后台事件没有反应
前台代码：

HTML code

<input id="Button1" type="Button" value="" runat="server" onserverclick="Login_click" style="background:url(images_login/dl.gif); border-style:none; width:49px; height:18px; background-repeat:no-repeat;"  />

C# code

protected void Login_click(object sender, EventArgs e)    {        string user = Request.Form["textfield"].ToString();        string pwd = Request.Form["textfield2"].ToString();        UM.userName = user;        if(UB.users_Query_by_Name_exist(UM))        {            Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('用户不存在！');</script>");        }        else        {            DataSet ds = UB.users_QueryUserDetail_by_Name(UM);            string EnPwd = ds.Tables[0].Rows[0]["password"].ToString();  //解密前的密码            string DePwd = DESEncrypt.Decrypt(EnPwd);                    //解密后的密码            if(DePwd!=pwd)            {                Page.ClientScript.RegisterStartupScript(Page.GetType(), "message", "<script language='javascript' defer>alert('密码错误，请重试！');</script>");            }            else            {                Session["user"] = user;                Response.Redirect("Admin_Index.html");            }        }    }

HTML code

    <form id="form1" runat="server">    <div>        <input id="btnLogin" type="Button" value="登录" runat="server" onserverclick="Login_click" />    </div>    </form>