Delete the preview cache. Have your operating system search for folder(s) whose name ends with Previews.LRDATA and delete these folder(s) (but not Smart Previews.LRDATA or anything else).
Open the folder that contains your Lightroom catalog. Locate and delete the folder that has the extension .lrdata. Then start Lightroom again. Lightroom will start building a new preview folder.
Please go to the location where your Lightroom Catalog is saved, and from there please delete the Folder Lightroom Catalog Previews.Lrdata.
Launch Lightroom , and let us know if it works.
Thanks so much! Problem solved