It sounds like you may have moved files or folders with Windows Explorer or anther program outside of Lightroom. This will cause the files to show as missing in LR with a ? on the image or folder.
As explained image files don't actually get "moved" when imported into LR. LR merely records the path where the file is located on your hard drive(s) in the catalog. If you "move" the files outside of LR it can create the situation you are experiencing.
If you haven't done a lot of editing to the files in LR the simplest solution would be to create a new catalog and import ALL of the image files you want to edit in LR. Notice I said "want to edit" and not "want to move." It is possible to move files on import LR, but I suggest not doing that. Your options are Copy, Move, and Add. You want to use 'Add' for images that are already stored on your hard drive.