Gridview pagination is not working??

I'm using pagination for my gridview ,I can able to click on next page at first time but second time it's not working but I checked by using break point ,in runtime am getting the pagination in pageindexchanged event.If I check with out break point the pagination is not at all working.Can any one help me how to solve this error.Here is my code

 

In PageLoad :

                      if(!IsPostback)

                       {

                         BindData();
               } 

BindData()

{

 string s="Select *from Tbl_Candidates";

SqlConnection con=new SqlConnection("Here is my connection");

SqlDataAdapter da=new SqlDataAdapter(s,con);

DataSet ds=new DataSet();

da.Fill(ds);

empGrid.DataSource=ds.Tables[0];

empGrid.DataBind(); 

 } 

 

{ 

   empGrid.PageIndex=e.NewPageIndex;

BindData(); 

}