Hello and welcome to JA.
The Simple Tech 160, is considered a legacy product. More info can be found here, on their website for legacy devices.
I can find the software for you, but you would have to tell me WHICH hard drive you have. Visit the above link, and pick out the drive you have, and let me know. I will then find the software, and provide you the link for download.
Or you can contact HGST directly ( I can not do this on the actual customers behalf) and request a physical CD/DVD be sent to you. Typically there is a small fee.
What happens, when you just plug in the hard drive? Does the computer recognize the drive?
What program were you using to do the backup? Was the program you were using to do the backup, come on the original disc, that you can no longer find now?
Honestly, you should NOT need any software to use an external hard drive that is USB. All you need to do is plug it in, and windows should auto recognize. Then you can use windows backup utility to run backups to that drive ............Done.
But if you absolutely have to have the original software, then I need to know the exact model and type, including date of purchase (just the year) so I can narrow down what you need.
Are you still needing help with this issue?