Thank you for this advice, but as stated in my post, I already tried that and it did not work.
Now I have even reset windows and installed a new Lightroom and I have the same issue.
It is really annoying to pay for something that doesn't work...
Did you carry out a reboot (NOT shut down and restart) between removing, installing ... between every new process that involves any kind of setup?
On Win 10, this really is needed because of it's Fast Startup option that is turned on by default.
Yes, I did reboot the machine.
I actually found the problem and the solution.
The problem was I couldn't install visual C++ 2010. (still don't know the reason though).
Find this hidden folder: C:\ProgramData\Microsoft\Crypto\RSA\S-1-5-18
rename it C:\ProgramData\Microsoft\Crypto\RSA\S-1-5-18_old
Install visual C++ 2010
Now Lightroom works
Happy for you that it works now.