Which version of Excel?
If 2010, try this:
Open Excel 2010.
Click on File > Options.
Select Trust Center > Trust center settings.
Select Protected view.
Uncheck all the options under Protected View > OK.
Restart Excel 2010 and try to open Excel documents.
Thread
HERE.
Good link
HERE.
Other Stuff.
Are you able to open it on another computer? Can you upload to Google docs and try from there?