Office 2013 executables got renamed with .bak extension

after applying microsoft updates about a week ago, office stopped working. finally saw that executables were all renamed w/.bak ext. i tried renaming, just comes up with an error and still none of the office apps. work. i wanted to reinstall, but having problems finding key code, used several 3rd party key code finder apps. but will not find 0ffice 2013. shows office 2013 is installed in control panel/programs. i need access to my calendar desperately.
thx cynthia

If you had bought Office Online, then check for the key in the E-mail you received from your retail seller..... if it's built in then you should have tried belarc advisor. if not read the article below my post. also you could backup you Office if in future anything happens to it.below is the link.
Download, back up & restore Microsoft Office products - Office.com
also you could try magical jellybean key finder.. it says it could recover office 2010 keys... hope it works on office 365.
KeyFinder | Magical Jelly Bean

Article:Quick Tip: Track down lost Microsoft product keys with ProduKey - TechRepublic

Thank you for replying, I have tried those key finders and am now trying "Product Key Finder" by Smart Key. None of them can find the key so far. I bought Office from a retailer that had the key on a little tiny piece of paper (no media), which of course I cannot find.