I am a having very serious problem with Microsoft Excel 2010. Well I have installed Window 7 on my computer. I have successfully installed Microsoft Office 2010 on my computer but there is no default program has been set for .xlsx file of the Excel 2010. Whenever I try to set default program for .xlsx file it prompts that unknown program. I have tried everything which I can do to solve the matter but it did not help me. Please give a suggestion to solve the matter.