Tried Recuva. Didn't work. Explorer says 1 TB drive is Healthy, 0% Fragmented, and no partitions when viewed through Disk Manager. What the heck? 400 GB I oughta see something. Want to try CCleaner 1-Pass Overwrite on top of the 35-Pass to see if it solves the problem but afraid I'll run out of disk space if this happens again.