In some cases date in Excel files can be in text format that uses variety of formats mm/dd/yyy or dd-mm-yyyy. There are plenty of examples on internet to convert any format to date. However most of the converters rely on fixed positions format.  (two for the date, two for the month, four for the year). It will not work  for dates that look like this 12/1/2012 because month has one position. In this case you need another converter that searches the text and finds the right position. In this post an example exce is provided. It contains a macro and a spreadsheet with an example.

Date_Convert