Thank you for your reply and greetings from upabove (Finland). I have now succeeded in getting xplane working again. I have installed it on D-disk (1 Tb) and my HP Omen has Intel i5-8400 16 Gb, 256 Gb SSD + 1 Tb HDD, NVIDIA GeForce GTX 1070 8 Gb.
However, I still have problems which I try to clear out with Aerosoft: The download process left out DVDs 2 and 7-9. There are several folders missing, such as XPUIPC. Cessna 172 flies without its rear end = tail, etc.
I have a back-up of my first xplane installation so I can compare the present installation with it.
I hope to get Aerosoft's replies soon.