In Excel 2003, dragging by handle does not increment the count!!

In my Excel 2003, selecting contiguous cells and dragging the handle of the last cell, used to increment the subsequent cells. Not any more!!. I select 3 contiguous cells with a range, suppose 1,2,3. Dragging the handle of cell containing ‘3’, should get 4,5,6… in subsequent cells. How do i get them? I tried Option but did not know what to tweak. Please reply at hirendra7158@gawab.com, too.
Thanks.