Login Password Case-Sensitive

 private void btnlogin_Click(object sender, EventArgs e)
        {
            login();
        }
        private void ClearFields()
        {
            txtusername.Text = String.Empty;
            txtpwd.Text = String.Empty;
        }

        private void btncancel_Click(object sender, EventArgs e)
        {
            this.Close();
        }
        private void txtpwd_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyValue == 13)
            {
                login();
            }
        }
        private void login()
        {
            try
            {
                ConnectionClass l_ConnectionClass = new ConnectionClass();
                DataSet l_UserDataSet = l_ConnectionClass.FetchDataInDataSet("select * from tbluserlogin where userName = '" + txtusername.Text.ToLower().Trim() + "' and userPwd = '" + txtpwd.Text.Trim() + "'");
                if (l_UserDataSet.Tables[0].Rows.Count > 0)
                {
                    PublicVariables.CheckLoginFlag = true;
                    PublicVariables.OSUserID = Convert.ToInt16(l_UserDataSet.Tables[0].Rows[0]["userId"]);
                    PublicVariables.UserRole = l_UserDataSet.Tables[0].Rows[0]["userRole"].ToString();
                    DateTime getdatefrm = l_ConnectionClass.getlogouttime();
                    DateTime datenow = DateTime.Now;
                    if ((getdatefrm.AddMinutes(0) > datenow) && (getdatefrm != DateTime.MinValue))
                    {
                        MessageBox.Show("please wait");
                        ClearFields();
                        PublicVariables.CheckLoginFlag = false;                  
                    }
                    else
                    {
                        l_ConnectionClass.updateuserlogin();
                        Close();
                        this.Hide();
                    }
                }
                else
                {
                    MessageBox.Show("Login Failed !!!!", "Error", MessageBoxButtons.OK);
                    PublicVariables.CheckLoginFlag = false;
                    txtusername.Text = "";
                    txtpwd.Text = "";
                    txtusername.Focus();
                }
            }
            catch (Exception ex)
            {
                MessageBox.Show("Connection Failed. Plz Check your Network Cable Connection", "Error", MessageBoxButtons.OK);
            }
        }
        private void txtusername_KeyDown(object sender, KeyEventArgs e)
        {
            if (e.KeyValue == 13)
            {
                txtpwd.Focus();
            }
        }