Option 1:
Right-click on the Excel file, choose Open With, click Choose Program...click Microsoft Excel from the list, check the box 'Always use the selected program to open this kind of file' and click OK.
If that doesn't help - Option 2:
Go to... Select Tools -> Options -> General tab and Uncheck "Ignore other applications"
Option 3:
Be sure to close the Excel. Go to Windows Start Button -> Run and type "excel /unregserver"
then in similar manner ....Windows Start Button -> Run and type "excel /regserver" ... that will reset some excel registry settings to defaults.
Option 4:
go to Tools -> Options -> General tab and make sure that the "At startup, open all files in:" is empty.
If nothing help - try these suggestions
In additional you may find helpful Microsoft recommendations to repair corrupted files - http://office.microsoft.com/en-us/excel/HA010346561033.aspx
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