Microsoft Office 2007 product key questiono

Hello,

I purchased an acer extensa from a 'laptop depot' in Calgary. The salesman told me the computer included Microsoft Office 2007 and is running Windows Vista Home SP1. At first Office worked fine and now it is asking for a product key. I did not get any disks with the computer (not something i noticed until i needed one). When i went back to the laptop depot they claimed that the disk would have been in the package (which was sealed). Now i don't know where to get another product key or how to find one... I still have my reciept and packaging..... Any ideas?