Have you seen below article?

http://www.techrepublic.com/blog/10-things/10-ways-to-recover-a-corrupte...

It has described top 10 ways to recover data from corrupt Excel workbook.

If nothing works for you, you can try generic Excel repair tools.

If you don't mind to pay for recovery of your data then I recommend Stellar Excel repair.

I came across this issue . An update to the Office Compatibility Pack that was still on a computer caused the default PROGRAM for .docx and .xlsx files to be the Microsoft Open XML Converter program and make the "Default Programs" in Control Panel think that Excel and Word were actually the Microsoft Open XML Converter scholarship essay writing assistance program as well.
UNINSTALLING the Office Compatibility Pack in Programs and Features and then a simple reboot fixed the issue.

Also:

1: Try to repair it manually when MS Excel does not automatically STARTS File recovery mode.

Click the Microsoft Office Button, and then click OPEN.

Now select the corrupted workbook that you want to open.

Click the arrow NEXT to the Open button, and then click Open and Repair.

Choose either Repair (to recover as much of the FILE data) or Extract data (to extract values and formula when repair process is not successful).

2: Open with Open Office: Try to open your Excel file in Open Office. It is an open-source Office suite that is able to open & SAVE Microsoft Excel files.

3: Save in HTML Format: Open your Excel file and save it in HTML format. By saving the workbook in HTML format, you may be able to filter out the corrupted elements.

4: Save in SYLK Format: Open your Excel file and save it in SYLK format. By saving the workbook in SYLK format, you may be able to filter out the corrupted elements.

See more on this site:
https://social.technet.microsoft.com/Forums/office/en-US/aecedc3e-d1d6-4...

Regards!