range of cells selected when I click on one
 

New to Excel 2007. I have many worksheets that I have a frequent but
intermittent problem with. When I click on a cell to select it, several seem
to group together like a range (no range is specified), usually below the
cell I click on. It does not always 'grab' the same number of cells, and
there is no pattern about data in the cells, etc. I then have to use the
arrow keys to get out of the range and to a single cell that I need. Any
ideas on what to check?