帮看一下哦。。谢谢各位
protected void Button1_Click(object sender, EventArgs e)
  {
  SqlConnection con = new SqlConnection("server=localhost;Initial Catalog=luntan;Integrated Security=SSPI;uid=;pwd=");
  try
  {
  con.Open();
  }
  catch (Exception ex)
  {
  throw ex;

  }
  string strcom;
  strcom = "select count(*) from USERS where USERNAME='" + TextBox1.Text + "'and USERPWD='" + TextBox2.Text + "'";
  SqlCommand com = new SqlCommand(strcom, con);
  int a=Convert.ToInt32(com.ExecuteScalar());
if (a > 0)
{
Response.Write("<script>alert('恭喜您登录成功！');location='javascript:history.go(-1)'</script>");
  Session["UserName"] = this.TextBox1.Text;
  Session["UserPwd"] = this.TextBox2.Text;
  this.Literal1.Text = Session["UserName"] .ToString()+ " " + "登录成功";  
  this.TextBox1.Text = "";//填写用户名的textbox
this.TextBox2.Text = "";//填写密码的textbox[/color]
}
else
{
  Response.Write("<script>alert('很遗憾，登录失败！');location='javascript:history.go(-1)'</script>");

}
  con.Close();
 
  }
登陆以后不能清空用户名和密码啊？这事什么原因啊？我是这样清空的
this.TextBox1.Text = "";//填写用户名的textbox
this.TextBox2.Text = "";//填写密码的textbox
还有this.Literal1.Text = Session["UserName"] .ToString()+ " " + "登录成功"; 这一句也不能显示
原来是可以清空的，因为是一边看书一边试，不知道什么时候他就清空不了了，不知道是不是自己该了什么东西！

------解决方案--------------------

C# code

//把location...去掉
Response.Write("<script>alert('恭喜您登录成功！');'</script>");