If you moved the photos so the relative folder structure is the same and the only thing different is the top-level drive-letter, device and/or folder path is different, the see here:
Basically, you have to relink the top-level folders to the new hard-drive location and you’ll be back in business.
They are already in the catalog. All you have to do is tell LR where they are. In the Library module right click on the drive name in the Folders area and select "Update Folder Location". Point it to the new drive.