Did you by any chance create a new Catalog? Catalogs are the containers that hold the media in EO. You can verify the same by launching EO and going to File->Manage Catalogs. Please see if changing the catalog to a previous version helps. If not, then we might need to investigate the issue further.
Also, this forum is ideal for Premiere Elements related queries. You can try Photoshop Elements for PSE related queries.
Also, don't forget to select the Back or Show All button at the top left of the Organizer's Media Browser -- just in case you've inadvertently filtered your media files.