I don't see the PowerPivot ribbon when I open my Excel file

Hi,

I have a problem with PowerPivot in Excel 2010. When I open just Excel without open a file, I see my add-in. but when I double click in a file to open it, I don't see the PowerPivot ribbon in Excel. I read a lot of discussion group but I didn't find anything. So, can you help me please?

Regards.