After using the same hard drive to store data [avi. mp4 mkv] for the last few years I developed a problem that when you click on a folder file, it doesn't open and asks you to format the file/hard drive. So I started to transfer the files to another hard drive some copied/moved OK, others wouldn't copy/move at all. After a while the hard drive was no longer accessible and all data was lost. Today I tried to copy files to a different hard drive, all worked OK, but when I tried to open the file folders, it started to happen again. Is this a problem with the computer or hard drives - I've run virus software on the computer and the individual hard drive but nothing has shown up. Any help would be appreciated.