Excel 2010 filter

[ddhelp]

I am not able to view the "search box" for filter in excel 2010.
http://blogs.office.com/b/microsoft-excel/archive/2009/10/01/excel-2010-new-search-filter.aspx

Is there a way to activate it? It appears and disappears on its own...

please help

Thanks

 

[Sektor]

Check, whether sheet is locked, or there's now empty row in data.

 

[ddhelp]

The sheet is not locked and there is data in all cells of the column.