Datatable showing only first values uploaded in the grid

protected override void OnColumnHeaderMouseClick(DataGridViewCellMouseEventArgs e)
      {

          if (dataSource == null)
              dataSource = (DataTable)this.DataSource;

          positionX = e.X;
          positionY = e.Y;

          bool flag = false;
          for (int columnCount = 0; columnCount < dataSource.Columns.Count; columnCount++)
          {
              if (!flag)
              {
                  positionX = positionX + this.Columns[columnCount].Width;
                  if (this.Columns[columnCount].Name == this.Columns[e.ColumnIndex].Name)
                      flag = true;
              }
          }
          positionX = positionX - this.Columns[0].Width;

          if (e.Button == MouseButtons.Right)
          {

              ContextMenu filterContextMenu = new ContextMenu();
              if (filterColumnList.Contains(this.Columns[e.ColumnIndex].HeaderText))
              {
                  columnName = this.Columns[e.ColumnIndex].HeaderText;

                  ArrayList columnFilterList = new ArrayList();
                  for (int count = 0; count < dataSource.Rows.Count; count++)
                  {

                      try
                      {
                          if (!columnFilterList.Contains(dataSource.Rows[count][columnName].ToString()))
                              columnFilterList.Add(dataSource.Rows[count][columnName].ToString());
                      }
                      catch
                      {


                      }
                  }
                  columnFilterList.Sort();





                  for (int count = 0; count < columnFilterList.Count; count++)
                  {
                      MenuItem uniqueColumnsMenuItem = new MenuItem();
                      uniqueColumnsMenuItem.Name = columnFilterList[count].ToString();
                      uniqueColumnsMenuItem.Text = columnFilterList[count].ToString();

                      if (checkedFilterHashTable.Contains(columnName))
                      {
                          if (((ArrayList)checkedFilterHashTable[columnName]).Contains(uniqueColumnsMenuItem.Text))
                              uniqueColumnsMenuItem.Checked = true;
                          else
                              uniqueColumnsMenuItem.Checked = false;
                      }

                      uniqueColumnsMenuItem.Click += new EventHandler(menuItem_Click);
                      filterContextMenu.MenuItems.Add(uniqueColumnsMenuItem);
                  }

                  filterContextMenu.MenuItems.Add("-");
                  MenuItem clearThisFilterMenuItem = new MenuItem();
                  clearThisFilterMenuItem.Name = "Clear This Filter";
                  clearThisFilterMenuItem.Text = "Clear This Filter";
                  filterContextMenu.MenuItems.Add(clearThisFilterMenuItem);
                  filterContextMenu.MenuItems.Add("-");

                  MenuItem clearAllFilterMenuItem = new MenuItem();
                  clearAllFilterMenuItem.Name = "Clear All Filters";
                  clearAllFilterMenuItem.Text = "Clear All Filters";
                  filterContextMenu.MenuItems.Add(clearAllFilterMenuItem);

                  clearThisFilterMenuItem.Click += new EventHandler(menuItem_Click);
                  clearAllFilterMenuItem.Click += new EventHandler(menuItem_Click);

              }

              filterContextMenu.Show(this, new Point(positionX, e.Y));
          }
      }