Excel 2007 : Date sorting..

I have recently done a large database including date entries. I wanted to finish the database and then add sorting filters. The problem is I realized too late that excel does not recognize dates written in this format "30.12.2012" (with dots between the numbers) and it gives me the option to sort them only from A to Z. Is there any way to change the whole column of dates without changing them one by one?

Thank you in advance