strange things happening in my spreadsheet, need some help

I have an excel file that was emailed to me from our accountants. Whenever I try to type a date in a cell, for example if I type 12/31/01, instead of automatically converting it to a date, 12/31/2001, it puts an = sign in front and returns =12/31/1, or .387096774. This doesn't happen in any of my other spreadsheet files. Why is it doing this with this file, and how can I stop it?

Thanks,
Kevin