problem on datagridview rowheader value not visible

before this for loop i set the datasource to datagridview. full code is
DataTable result= userdao.getdateanddayfortimetable1(comp);
DataTable period = userdao.getperiodfortimetable();
int periodcount = period.Rows.Count;
int daycount = result.Rows.Count;
DataTable dt = new DataTable();
for (int i = 0; i < periodcount; i++)
{
dt.Columns.Add();
}
for (int j = 0; j < daycount; j++)
{
dt.Rows.Add();
}
//System.Windows.Forms.DataGridView grid = new System.Windows.Forms.DataGridView();
PLayer.GenerateTimetable gt = new PLayer.GenerateTimetable();
// gt.dataGridView1.DataSource = dt;

for (int k = 0; k < periodcount; k++)
{
//gt.dataGridView1.Columns[k].HeaderText
dt.Columns[k].ColumnName= period.Rows[k]["PeriodNo"].ToString()+"(" + period.Rows[k]["StartTime"].ToString() +"-"+ period.Rows[k]["EndTime"].ToString() + ")";
}
PLayer.TimeTable timetable = new PLayer.TimeTable();
timetable.timetablegrid.DataSource = dt;
//for (int m = 0; m < daycount; m++)
//{
// string rowheader = result.Rows[m]["Working_day"].ToString();
// timetable.timetablegrid.Rows[m].HeaderCell.Value = rowheader;

//}
for (int i = 0; i < daycount; i++)
{
//System.Windows.Forms.DataGridViewRow row = new System.Windows.Forms.DataGridViewRow();
//row.HeaderCell.Value = result.Rows[i]["Working_day"].ToString();
timetable.timetablegrid.Rows[i].HeaderCell.Value = result.Rows[i]["Working_day"].ToString();
}


timetable.Show();

in this first two datatable contains data for setting columnname and rowheader and how many row and column need to be create. here i already set column name but i cannot able to set rowheader. even i try the following code for checking
timetable.timetablegrid.Rows[i].HeaderCell.Value=(i+1).ToString(), still it does not work. but the same code working in another gridview for rowheader text. thats why i am stuck here.

sorry i stuck with this problem from yesterday.
when i go through the code in for loop, it set the row[i].headercell.value to the particular string.but when datagridview shows, row header text not appear. i check all the properties and i confused why in this gridview only not showing text in row header