Missing images, files, folders, content

Help please. When I open a catalog, images may or may not appear. File locations are all lost. And, opening a new catalog results in same similar issues. It appears LR only stores and/or looks for images in the user's picture folder. Specifically:

1. Opening existing catalog:

a. In one catalog, file names recognized but no images. LR can't locate image files. (.dng or raw)

b. In another catalog, can see images, but can't locate them as above.

c. Go to import, says it cannot find target folder and defaults to picture folder.

2. Create new catalog but when go to import, it cannot find catalog or target folder I just created and defaults to picture folder.

All image files and folders and .lrcat files exist in correct locations on disk and can be located. Opening Lightroom catalog by clicking directly on catalog file opens catalog but files and folders remain unlocated.

Please help. This is a major problem.