We have a huge spreadsheet containing various pieces of information about
files. One of the columns contains a date. The column is formatted as
Date. However, for some inexplicable reason the date in this column is now
showing as just digits. If you double click on the cell it displays the
date as it should be seen, i.e.

40634 = 01/04/2011
37834 = 01/08/2003
37926 = 01/11/2003

Can anyone explain why, please. Also, it doesn't matter how I format that
particular column it refuses to display the date as a date.