Forms Data Controls :: Update Mark And Convert To Template Field

Im using agrid view which does not using sql datasource and im trying ro Update it this is the Code:

public partial class senior_MarksApproval : PageDataAccess
{
protected void Page_Load(object sender, EventArgs e)
{
Title = "View Marks Approval Requests";
if (IsPostBack)
{
DataTable Ds = DA.getSemester();
lblsem.Text = Ds.Rows[0]["SemID"].ToString();
BindGrid();
}
}
void BindGrid()
{
DataTable DT = DA.GetMarksReqApproval(Convert.ToInt32(DropDownList1.SelectedValue), Convert.ToString(DropDownList2.SelectedValue));
GridView1.DataSource = DT;
GridView1.DataBind();
}
protected void GridView1_RowUpdating(object sender, GridViewUpdateEventArgs e)
{
String CID = GridView1.DataKeys[e.RowIndex][0].ToString();
String STDNo = GridView1.DataKeys[e.RowIndex][1].ToString();
String Mark = ((TextBox)GridView1.Rows[e.RowIndex].Cells[2].Controls[0]).Text;
DA.EditMarks(CID, STDNo, Convert.ToInt32(Mark), DateTime.Now.ToString());
GridView1.EditIndex = -1;
BindGrid();
}

I want To update Mark and i convert it to template Field ,When I press Update I get the Old value not the Newest One of The Mark and nothing were Updated Except The Date Value in each DataBase and Grid