In response to your questions:
Yes, I mean hard drives as follows:
(1) Internal - SanDisk, c: drive, 1.79 TB - rotational (conventional)
(2) External - Seagate Backup, f: drive, 2.27 TB - rotational (conventional)
(3) Internal - ST2000DM001, d: drive (HP recovery drive) - rotational (conventional)
Note that I uninstalled the program and reinstalled it, where the original parameters where already known - i.e. did not ask for the product key, and previous activities were known, e.g., the first hardware diagnostic was incomplete. Still getting the problem!
Note: When I first installed the program all drives were recognised. I then conducted a basic diagnostic, all worked fine except that c: drive could not be completed due to activity. Since then the drives are not listed.
Also note that I got the version for the 64bit OS.
After the Toolbox application was closed, the task manager showed that the following are NOT running: pcdrcui.exe or pcdrrealtime.p5x.
Finally, and not too sure, it seems that the program also hangs my computer on a restart! Uninstalled once again - system is working fine...