Lost entire engine os database

hmmm… just lost my entire engine os 421 database… it seems engine no longer knows about my hd with all my music… win11 still shows it 'n says its there [no errors], so does engine if i look at the folder tab on the left… but my collection now says 0 tracks… i tried restoring from a backup a week ago [ive made no changes since] but it also says 0 tracks… looks like i need to rebuild the db - all files still exist on my ext hd, as does the collection structure ie smart folders n playlists… they are just all empty.