Assume that you install the new Microsoft Office on a computer that has Office 2010 installed. When you double-click an .xslx file on the computer, Excel 2010 starts but the workbook does not open.
To resolve this issue, apply the following hotfix package:
2687347 Description of the Excel 2010 hotfix package (Excel-x-none.msp): August 28, 2012
Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.