student information form givning an error

<configuration>
  <configsections>
    <connectionstrings>
      <add name="ConString" connectionstring="Data Source=ANAND;Initial Catalog=TEST;Integrated Security=True"
           providerName ="System.Data.SqlClient"/>
     </connectionstrings>
  </configsections>
</configuration>

using System.Data;
using System.Data.SqlClient;
using System.Configuration;
namespace Studentinformation
{
    class DB_Access
    {
        SqlConnection conn;
        public DB_Access()
        {
            conn = DB_Connection.GetConnection();  // in this line the runtime error is rise
         }
        public void add_student(string regNo, string fName, string Lname, string phoneNo)
        {
            if (conn.State.ToString() == "Closed")
            {
                conn.Open();
            }
            SqlCommand newCmd = conn.CreateCommand();
            newCmd.Connection = conn;
            newCmd.CommandType = CommandType.Text;
            newCmd.CommandText = "insert into student values('" + regNo + "','" + fName + "','" + Lname + "','" + phoneNo + "',)";
            newCmd.ExecuteNonQuery();
        }
    }
}

class DB_Connection
   {
       public static SqlConnection NewCon;
       public static string ConStr = ConfigurationManager.ConnectionStrings["ConString"].ConnectionString;
       public static SqlConnection GetConnection()
       {
           NewCon = new SqlConnection(ConStr);
           return NewCon;
       }
   }

public partial class Form1 : Form
   {
       public Form1()
       {
           InitializeComponent();
       }

       private void btnAddNew_Click(object sender, EventArgs e)
       {
           frmNewStudent newstudent = new frmNewStudent();
           newstudent.Show();
       }
   }