Ended up going way, way back to win 8 as this was original OS (back to 2013!) via some samsung recovery program, then c.150 updates. Now going to 8.1, & then I'll try win 10. So looks like windows has decided on the incremental approach.
At least the laptop is working fine & dandy, so looks like there are no hardware issues, thankfully.
Re-installed 1809 but it failed on second boot part of the install. Checked on samsung site & seems it (ativ 8) should be able to handle 1809, which did come originally from win update, & not through me forcing it. Previously it's been running absolutely fine on 1809.
Reluctantly gone back to win 8.1 (c/w classic shell) & machine functions fine. No problems on boot at all. Just a bit disappointed I can't have my win 10 back, & now have to re-install all programs.
No, 1st boot spinning dots fine, then they locked up at 2nd boot part of the install process & wouldn't progress to full boot up. Sorry should have been clearer but a lot happened during install, but then nothing happened, if you know what I mean...
Getting a bit concerned with this as it's proving to be unreliable on booting with win 8.1 now. Sometimes it boots straight away & operates ok, others after maybe 1/2/3 attempts. I'm sure SSD is ok as that's the newest component fitted a couple of years ago. I've ran all previous mentioned tests and all came back clear. What next? CMOS battery or mobo problem? Cheers.