Date displays as serial number. Cannot format to display as date

[SunnyG]

Went in to modify an existing spreadsheet. The date fields are displaying as
serial numbers. Had been displaying properly as dates. Have not been able
to format so field displays as a date unless I format it as text. Any
suggestions on how to correct?

 

[ufo_pilot]

Format>Cells>Custom
then try a variation of what you would like to see (dd-mmm-yy or
ddd-dd-mmmm-yyy....etc)
Keep your eye on the Sample and see what you need