Lightroom save the default catalog file in Picture folder on the local hard drive.
Close Lightroom and Open Lightroom while holding down the Alt/option key and it will show all recent catalog used in Lightroom, select the right catalog and open it.
Go to Picture's folder on the local disk >> Look for Lightroom folder >> Click Lightroom catalog file (.Lrcat)
Let us know if that helps.
I did that but all my images have the exclamation point on them saying the file cannot be located. I have always imported new images into Lightroom and have not always backed them up.