First check weather the method is filling data table or not. Declare a debug point on line 2 of code in my case. If your DataTable is empty than it will not show you gridview.
DataTable dataTable = new DataTable();
dataTable = gettingDataFromSomeMethod();
GridView1.DataSource = dataTable;
GridView1.DataBind();
One more thing you can do is give ShowHeader attribute to gridview so atleast your header will be visible inspite of, whether your datatable is empty of filled.
<asp:gridview id="GridView1" runat="server" showheader="true" xmlns:asp="#unknown" />