Several Folders and Files on my external hard drive (Seagate, 1 tb) have disappeared. Those do not show up on explorer. Disk space utilization apparently indicates more space utilized than list of files shown (excess utilization to the extent of 250 gb). I tried Recuva but it recovered only deleted files I had consciously discarded. After moving the few visible files to another drive, I backed up the EH disk, formatted it and then restored its contents back to the formatted EHD. Now explorer says there are no files on the disk but about 250 gb space is used up in the disk. During the process of backing up and restoration, I noticed the names of missing files and folders being flashed on screen - those files are apparently occupying disk space but not showing up in the explorer window (even after ticking the 'show hidden files' option) and I am unable to access to any of those files / folders.

MSE / Malware bytes did not show up any malware / virus during scans of the drive. Is there any way I can make those invisible files to reappear?