Comprehensive source:
http://www.filerepairforum.com/forum/microsoft/microsoft-aa/excel/481-excel-files-corrupted – must be helpful to you, forum contains some interesting thoughts about excel files
How to Recover an Excel Auto-Save File
Enable Excel's Auto-Save Feature
1. Open "Microsoft Excel."
2. Click "Tools" from the top navigation bar, and then select "Add-ins."
3. Click "Auto-Save" and edit any of the optional items. Click "OK." The auto-save feature is now enabled.
Using Excel Auto-Save Recovery
4. Open "Windows Explorer," and locate the Excel file's temp file to recover. This file will be saved in the same directory as the originally saved Excel files. In the event of a power failure or other issue, the file may not auto-save in the same location. Find the temp file, which will also be saved in one of the following directories, where "username" is the current user's access ID:
"C:\Users\<username>\AppData\Local\Temp"
or
"C:\ Documents and Settings\<username>\Local Settings\Temp"
Temp files are prefaced with a tilde (~).
5. Double-click on the file to recover. The file will open in Excel and automatically enable the Auto-Save Recovery feature. Click "Recover" to recover the document.
6. Save the temp file in Excel. The file has now been recovered.
If previous solutions aren’t helpful to you, try to use
Excel Repair Toolbox
Demo version:-
http://www.excelrepairtoolbox.com/</username></username>