Hey there again, @roverit!
Have you tried the link with the tutorial I provided in my previous post? Taking ownership of the drive in Windows should help you make the SSD accessible. If not, you should check how it appears on another computer and attempt to take ownership from there as well. If nothing works, I'd even suggest plugging it externally via a SATA-to-USB cable or an enclosure to see how it will get recognized by the system then.
Good luck. Let us know how it goes.
SuperSoph_WD