Reinstating your catalog
The catalog (or catalogs) is saved to a computer's hard drive by default, although it can be saved to any drive, even a removable one.
Catalogs should be backed up on a regular basis (use the Organizer | File | Backup Catalog command to do this), preferably to a removable drive or even to the cloud. Never back up to the same drive that you use to run Elements from because that wouldn't really be a true backup. Always back your catalogs up to a different drive.
I know the prospect of backing up is boring, but trust me, you only have to lose everything once – whether to a mechanical or electronic failure, or even a virus – to fully appreciate how important the simple process of backing up can be.
So, how do we reinstate a catalog if we suffer data loss? The first thing is to make sure that the computer is 100% virus- and problem-free. There is no point in risking the loss of your data a second time if the computer is not fixed...