Opening Window form using timer?

Question

Process:
I am having a table 
s.no ID_1 ID_2 content 
1 1001 4001 Hi
2 1002 4002 Hello
 
I used timer to bind this table in gridview of windows form
using the same timer i checked whether there is any content for the _ID2 from the table.
If the content value is true a new window form should be displayed.
 
Issue facing:
Each and every time the timer gets load it displaying the new windows even it is opened for the same _ID already how to check the form is open for the _ID which is opened already?
 

My code:
private void timer1_Tick(object sender, EventArgs e)
{
try
{
string Msg = string.Empty;
int Suc;
string tmpSuc = string.Empty;
string i;
string Role = Form1.role.ToString().Trim();
XmlNode Node;
int tmpSid;
string tmpChat = string.Empty;
wsTestService.STUDENTS_ONLINE(Role, out Node, out Msg, out Suc);
DataTable dt = new DataTable();
dt.Columns.Add("Students_Name", typeof(string));
dt.Columns.Add("ID", typeof(int));
dt.Columns.Add("Status", typeof(string));
foreach (XmlNode node in Node)
{
DataRow dr = dt.NewRow();
dr["Students_Name"] = node["Name"].InnerText;
Student_Name = Convert.ToString(dr["Students_Name"]);
dr["ID"] = node["ID"].InnerText;
tmpSid = Convert.ToInt32(dr["ID"]);
string chtdtm = "MM-d-yyyy";
string date;
wsTestService.CHAT_RECEIVE_MESSAGE(tmpSid, Tutor_ID, out tmpChat, out date, out tmpSuc);
DateTime today = DateTime.Today;
//chtdtm = Convert.ToDateTime(chtdtm);
string tmpdate;
tmpdate = today.ToString(chtdtm);
if (tmpChat != string.Empty)
{
if (tmpdate == date)
{
do
{
Chat_Box_Test objCTB = new Chat_Box_Test();
Chatting = tmpChat;
objCTB.Show();
} while (Student_ID == tmpSid);
}
}

 
//Chatting = tmpChat;
Student_ID = tmpSid;
i = node["Status"].InnerText;
if (i == "true")
{
dr["Status"] = "online";
}
else
{
dr["Status"] = "offline";
}
dt.Rows.Add(dr);
}
dataGridView1.DataSource = dt;
}
catch (Exception)
{
 
throw;
}

}