Retrieve lost iPhoto after replaced hard drive I replaced the hard drive on my MacBook Pro through Apple. I backed up files on my computer but not my Applications.

Is my iPhoto lost forever? I have thousands of pictures on there! I've signed in to iCloud and the iPhoto icon is not ticked. Is everything lost? Can I call Apple and retrieve my old hard drive somehow?
If you backed up all your files, then your library has been backed up and all you are missing is the iPhoto app. The iPhoto app has been replaced by Photos.app in Yosemite, so you can re-download iPhoto or Photos from the Mac App Store and your library will be automatically detected.

If you didn't back up all your files, then you need to rely on the last one thousand photos accessible in Photo Stream or Shared Photo Streams.