All my files and pictures got lost or deleted while installing the OS X El Capitan software All my files and pictures got lost or deleted while installing the OS X El Capitan software! Is there a way to get at least my iPhoto Library back? I have not made a back up before. 

Thanks for your help!
You can try a recovery software like wondershare recovery data or Disk Drill (i think you can download free trial), Those soft will be able to detect lost data (even deleted). There are many other soft you can test, but those two are great !

Hope this will help,

Peace