Try this:
DataTable Dt = (DataTable)(GridView1.DataSource);
Dt.Rows.Add(Dt.NewRow());
Dt.Rows[Dt.Rows.count-1]["ColName"]=txtProd.Text;
Dt.Rows[Dt.Rows.count-1]["OtherColName"]=txtCatgeory.Text;
Dt.Rows[Dt.Rows.count-1]["MyColumn"]=txtDescription.Text;
Dt.AcceptChanges();
GridView1.EditIndex = Dt.Rows.count-1;
GridView1.DataSource = Dt;
GridView1.DataBind();