@andrewnz yes, I have been through the things on that page, thank you :)

As an aside, it takes forever to download the ISO via the MCT.

I have a Fibre100 connection, but the download just trickles down at 3-4Mbps.

Should it be faster than that? I am the only pc doing any downloading today.

EDIT : I am wired not wifi.

In this case what I would do is take your dads SSD out of the laptop, plug it in another PC and then copy the personal data off it.

Then run produkey and manually select the reg hive of that disk to get the license.

Try to boot the SSD on the PC and see how far you get, if you can do a repair install, otherwise if not:

Put the SSD back in the laptop and run windows 10 setup, do a full reinstall,

What I suspect is wrong is the SSD is either on it's way out or the files on that install are so corrupted you can't fix it.

Good Luck.

Just did a test.... Windows ISO download... 25Mbps.... VDSL and 5Ghz WiFi....

This probably won't help, but over many Windows failures with many OS versions over many years, I have repeatedly experienced spurious and meaningless error messages that ended up having nothing at all to do with the actual problem. Windows seems to be particularly bad at triggering false and misleading errors. I can't say that is the case here, but I have learned the hard way not to take Windows error messages too seriously, especially when they involve boot errors. My most recent example of this is earlier this year when I started getting errors about files being corrupt during boot-up. After wasting a lot of time going down false trails I eventually narrowed the problem to a faulty SATA cable. After replacing that, all errors disappeared. The errors Windows reported had nothing to do with the actual problem and actually made it harder to pinpoint. I would have got there much sooner if there had been no error messages. This is not the first time I have experienced something like this. The problem is that it may focus your attention on a particular file that is not actually connected to the real problem. That may not be the case with you, but don't get too fixated on a particular file. The real issue may be somewhere else entirely.

Thanks @rikkitic , I will keep an open mind, while trying not to lose it completely. :)

I'm struggling to think of things that might actually help but it isn't easy with something like this. My experiences with Windows repair functions also haven't been that positive. They usually seem to do more harm than good. An added problem is if changes have been made to the drive while trying to repair. Everything that gets done makes it harder to get back to a place where you can actually fix the problem.

A nuclear option, which has worked well for me on older OS versions, but should only be attempted as an absolute last resort, is just to overwrite the boot sector of the drive. This may work, it may make things worse. I should point out that I have no experience with Win 10. Here is a link you might find helpful, though: https://www.pcworld.com/article/3113585/windows/how-to-repair-windows-master-boot-record-and-fix-your-bricked-pc.html

Here is another: https://www.howtogeek.com/howto/32523/how-to-manually-repair-windows-7-boot-loader-problems/

Maybe also this, but note that you can really go down some rabbit holes so be sure you feel up to it: http://www.ntfs.com/recovery-toolkit.htm

Finally, if you do decide to try any of this, the best place to start may be here: https://neosmart.net/EasyRE/Features/

I have used neosmart many times for other things (their EasyBCD is brilliant) and they are trustworthy and reliable. 

Hopefully you can get somewhere with some of this.

hmmm, with all my tinkering I believe I am now in a worse position than when I started.

The Windows repair environment doesnt even start up now, just boots to a pale blue screen.

I have ordered a new SSD and will be installing from scratch.

Thanks everyone for your help and advice.