This is one of the most common, and certainly the most stress-filled request I get for help. You open up Lightroom, and there is nothing there — all the photos you have imported and worked on are gone. Fortunately, this usually isn’t the disaster that it at first seems to be.
When you are in Lightroom, you are looking at Lightroom’s catalog. You can read more about the relationship between the catalog and your photos in my earlier post, About Your Images and the Lightroom Catalog. In a nutshell, the catalog contains all the information about your photos, all the work you do on your photos, and some snapshots of your photos, but not the photos (original raw files, jpegs) themselves. If you open Lightroom and it is blank, you have a catalog with no information about any photos, but your photos are almost certainly still sitting safely on your hard drive as they were before.
Assuming you aren’t just starting out with Lightroom, why would the catalog be blank? It is usually because for one of various reasons, Lightroom forgot about or couldn’t find the one you were working with, and therefore opened up a blank new one. Often, in the menu bar you can go to File>Open Recent, and your “real” one will be in the list — simply select it to relaunch Lightroom with it. If there are no catalogs in the Recent list other than the one you are in (at the top of the list, with a checkmark next to it), then you will have to tell Lightroom where your catalog is. If you know where it is (perhaps you moved it), go to File>Open Catalog, and navigate to it — it will be an .lrcat file. Once you highlight it and click on Select, Lightroom will relaunch with this catalog.
If you don’t know where your catalog is, first check for it in the Lightroom folder within your Pictures folder. If it is not there, then out in Windows Explorer or Mac Finder, do a search of your hard drive for .lrcat files. Find the most recent one (based on the Date Modified) that isn’t in your Backups Folder. (Your search will bring up all of your catalog backups — it is best not to work with one of these unless you can’t find your main one. If you do have to work with a backup, copy it out of your backups folder first — perhaps into a folder called “Main Lightroom Catalog”.) Once you find the catalog in Mac Finder or Windows Explorer, a quick way to launch Lightroom with it is to double-click on it.
So that Lightroom always opens with the correct catalog, once you open Lightroom with the correct catalog, go to Lightroom>Preferences (Edit>Preferences on a PC), and on the General tab under When starting up use this catalog, choose your main catalog from the list in the dropdown (rather than load most recent).
The most common scenario that leads to this issue is when users move their Lightroom catalog to an external hard drive. In this post on moving your Lightroom catalog you will find information on how to to accomplish this so that Lightroom knows to look for the catalog there. After you set this up, you must remember to plug in your hard drive before you launch Lightroom. If you don’t, and when you get the warning message you click “use default catalog”, Lightroom will open up a catalog in your Pictures folder — and if there there wasn’t one there already, it will be a new one and will be empty.
Where can you turn if you need more help? I do offer private online instruction, which you can read about on this page. For free troubleshooting, I would turn to lightroomforums.net — a great community of Lightroom users and experts.