LIGHTROOM: Missing files on ThunderBay Raid Drive after internal Hard Drive crash
Lightroom doesn't store images in the Lightroom catalog, it only stores the editing metadata. If Lightroom can not locate the images, they may be missing (!) or simply not where Lightroom is expecting them. The first step is to manually locate your images to confirm they are still in place on your harddrive (or wherever you had them). If the images are NOT where you expect them, and you can not find them manually, you may have lost or destroyed the images.  Lightroom can not help recover the images, as it does not store the images in the catalog.

But if you find the images, then perhaps the Lightroom catalog has lost track of them, or they are in a renamed location (you changed the user name, which changes the top level directory in MacOS). The first step is to look at the menu tree on the left in the Library module. If any images or folders are listed as "missing' (with an exclamation mark: "!"), then inspect them to see what folder/drive they are attempting to connect to.  Make sure the location in Lightroom matches the location on your drive. 

This article is extremely good instruction on how to reattach images to the Lightroom catalog, and I will simply point you to it rather than reproduce all intricate instructions here. However, this article guides you on reconnecting images to the Lightroom catalog.