Page with GridView ASP.NET not display in browser - asp.net

Question

I try to bind data from code behind into a GridView. I don't know what's wrong cause there is no error from debug, but when I try to display the page in browser it doesn't display (the hole page won't come up).
<asp:GridView runat="server" ID="productCart" AutoGenerateColumns="false" EmptyDataText="There is nothing in your shopping cart." GridLines="None" Width="100%" CellPadding="5" ShowFooter="true" DataKeyNames="ProductId">
<HeaderStyle HorizontalAlign="Left" BackColor="#F36EA7" ForeColor="#FFFFFF" />
<FooterStyle HorizontalAlign="Right" BackColor="#6C6B66" ForeColor="#FFFFFF" />
<AlternatingRowStyle BackColor="#F8F8F8" />
<Columns>
<asp:BoundField DataField="Description" HeaderText="Description" />
<asp:TemplateField HeaderText="Quantity">
<ItemTemplate>
<asp:TextBox runat="server" ID="txtQuantity" Columns="5" Text='<%# Eval("Quantity") %>'></asp:TextBox><br />
<asp:LinkButton runat="server" ID="btnRemove" Text="Remove" CommandName="Remove" CommandArgument='<%# Eval("ProductId") %>' style="font-size:12px;"></asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>
<asp:BoundField DataField="UnitPrice" HeaderText="Price" ItemStyle-HorizontalAlign="Right" HeaderStyle-HorizontalAlign="Right" DataFormatString="{0:C}" />
<asp:BoundField DataField="TotalPrice" HeaderText="Total" ItemStyle-HorizontalAlign="Right" HeaderStyle-HorizontalAlign="Right" DataFormatString="{0:C}" />
</Columns>
</asp:GridView>
.cs:
public partial class Cart : System.Web.UI.Page
{
UserSingleton activeUser = UserSingleton.Instance;
List<CartItem_Test> CartItems = null;
protected void Page_Load(object sender, EventArgs e)
{
DataTable dataTable = Access.GetInfo("CartPerUserID", "*", "UserID=" + activeUser.get_user().ID);
if (dataTable.Rows.Count > 0)
{
CartItems = new List<CartItem_Test>(dataTable.Rows.Count);
foreach (DataRow row in dataTable.Rows)
{
CartItem_Test cartItem = new CartItem_Test(row);
CartItems.Add(cartItem);
}
}
if (!IsPostBack)
{
productCart.DataSource = CartItems;
productCart.DataBind();
}
}