Getting Macbook back to original
From: http://kevin.kevandisa.com/2013/04/how-to-restore-macbook-to-factory-settings/


  
  Start Computer up, holding OPTION key
  You should now see two hard drive icons, select the one labelled “Recovery”
  Select your language
  Click on Disc Utility
  Click on Macintosh HD
  Select the “Erase” tab
  Erase the Disc
  Now go back to OSX Utilities – Select “Reinstall OSX”
  The recovery setup should be smart enough to download the latest
  licensed
  Operating System for your computer (in my case it was Mountain Lion
   10.8.3)
  Reinstall to Macintosh HD
  


Also see: http://support.apple.com/kb/HT4718 and https://discussions.apple.com/docs/DOC-4571