I am donating old computers to a senior center. I have removed the drives, and installed them as slaves on a working computer. I used software like cyberscrub and stompsoft file shredder to totally clean them. On one drive , my personal documents are not deleting. The reason is that they may be write protected (they weren't) or that some application is currently using them - not! I tried multiple times, rebooting, safe mode, same files are stuck. I even held the drive next to a large speaker magnet. How can I wipe out this drive?