my guess would be that the file you have opened is identified as an "add-in" this will cause the file to be blank when opened (i presume that by "blank" you mean without any worksheets). to check this,
1) open up one of these files
2) open up the VBEditor (Alt+F11)
3) open the Project Explorer window (Ctrl+R)
4) in the Project Explorer window, look for a tree entitled VBAProject(YourFileNameHere.xls) (or .xla)
5) expland this tree by clicking on the + sign and then double-click on the folder entitled "Microsoft Excel Objects"
6) click on the line with the Excel icon entitled "ThisWorkbook"
7) open up the Properties window (Ctrl+R) and scroll down to the line "IsAddIn"
8) check to see if this is "True" or "False". you can change the state simply via the dropdown box (available upon clicking)
if IsAddIn is true, then this is causing the blank file.
hope this helps. ben.