Shredos Disk Eraser 64 bit for all Intel 64 bit processors as well as processors from AMD and other vendors which make compatible 64 bit chips. ShredOS - Secure disk erasure/wipe - PartialVolume/sh...
ShredOS is a USB bootable (BIOS or UEFI) small linux distribution with the sole purpose of securely erasing the entire contents of your disks using the program nwipe.
Back when I used to work for others, I would always remove the disk drive and replace it with an identical uet fresh out of the box one and a fresh Windows install. A few hundred dollars and a little work is a small price to pay.