gridview always insert mode

protected void Page_Load(object sender, EventArgs e)
    {

        lQry = "Select SNo from sample";
        ds = clsGen.GetData(lQry);
        GridviewSample.DataSource = ds;
        GridviewSample.DataBind();
        if (!IsPostBack)
        {
            GridviewSample.SelectedIndex = 0;
            //GridviewSample.Rows[0].BackColor = System.Drawing.Color.LightGreen;
        }
    }

protected void GridviewSample_SelectedIndexChanging(object sender, GridViewSelectEventArgs e)
  {
      GridviewSample.Rows[GridviewSample.SelectedIndex].BackColor = System.Drawing.Color.LightGray;
  }

protected override void Render(System.Web.UI.HtmlTextWriter writer)
   {
       foreach (GridViewRow row in GridviewSample.Rows)
       {
           if (row.RowType == DataControlRowType.DataRow)
           {
               row.Attributes["onmouseover"] =
                  "this.style.cursor='hand';this.style.textDecoration='underline';";
               row.Attributes["onmouseout"] =
                  "this.style.textDecoration='none';";
               // Set the last parameter to True
               // to register for event validation.
               row.Attributes["onclick"] =
                ClientScript.GetPostBackClientHyperlink(GridviewSample,
                   "Select$" + row.DataItemIndex, true);
           }
       }
       base.Render(writer);
   }

protected void GridviewSample_RowDataBound(object sender, GridViewRowEventArgs e)
    {
        if (e.Row.RowType == DataControlRowType.DataRow)
        {
            if (e.Row.RowState == DataControlRowState.Edit || e.Row.RowState == (DataControlRowState)5)
            {
                TextBox t1 = (TextBox)e.Row.Cells[1].Controls[0];
                TextBox t2 = (TextBox)e.Row.Cells[2].Controls[0];
                if (t1 != null & t2 != null)
                {
                    t1.Attributes.Add("onmouseover", "this.originalstyle=this.style.backgroundColor;this.style.backgroundColor='#DDDDDD'");
                    t1.Attributes.Add("onmouseout", "this.style.backgroundColor=this.originalstyle");


                    t2.Attributes.Add("onmouseover", "this.originalstyle=this.style.backgroundColor;this.style.backgroundColor='#DDDDDD'");
                    t2.Attributes.Add("onmouseout", "this.style.backgroundColor=this.originalstyle");
                }
            }
        }
    }

<asp:GridView ID="GridviewSample" runat="server" AutoGenerateColumns="false"
        onselectedindexchanged="GridviewSample_SelectedIndexChanged"
        onselectedindexchanging="GridviewSample_SelectedIndexChanging"
        SelectedRowStyle-BackColor="LightGray" ondatabound="GridviewSample_DataBound" >
    <Columns>
     <asp:BoundField DataField="SNo" HeaderText="SNo" />
    <asp:TemplateField HeaderText="Name">
    <ItemTemplate >
     <asp:TextBox ID="txtname" runat="server" ></asp:TextBox>
    </ItemTemplate>
    </asp:TemplateField>
     <asp:TemplateField HeaderText="Age">
    <ItemTemplate >
     <asp:TextBox ID="txtage" runat="server" ></asp:TextBox>
    </ItemTemplate>
    </asp:TemplateField>
    </Columns>
   </asp:GridView>