Buford T.,

"How about the situation when Windows can't find the hard drive?"

... or the PC/laptop is stolen, or the building it was in burned down, or the vehicle it was in got swept away in a flood, and so on... Point taken -- advertising hype. Data stored on most types of storage persists until overwritten, &/or in the case of memory, including SSDs, is cleared, e.g. by running Trim on an SSD. That data is stored in small chunks with a sort of table of contents recording what's stored where. When you can't use that TOC, say a file's been deleted or access is not allowed, those chunks of data can sometimes be retrieved & possibly pieced together to form files or snippets of data, which is the basis for some hacks & computer forensics. Do Your Data Recovery Pro & similar [e.g. the free Wise Data Recovery] read the chunks of data they find by scanning the entire storage you run them on, e.g. a disk partition, then attempt to assemble that data into files.

In the case of a regular hard drive or SSD drive not showing up in Windows Explorer, if the drive is also not shown in Control Panel -> Admin Tools -> Computer Mgmt., you'd probably want to follow the steps outlined here: seagate[.]com/support/kb/the-bios-does-not-detect-or-recognize-the-ata-sata-hard-drive-168595en/ . You'd start with the device BIOS to make sure the drive is both physically detected & connected, then make sure it was getting power and so on, but there's a fair chance all you'll accomplish is verify the drive's dead. If it's an M2 drive, you'd likely want to do more research based on the drive & motherboard brand/model -- it might be anything from compatibility issues to bad drive firmware to problems with the BIOS firmware etc.

Tony , you can install it on a USB drive (such E:/Do Your Data Recovery Pro 6.8) but you will only be able to run it from that USB drive and only on the computer you used to install it. It is not a portable version you can have in your USB and use on any computer.