Gerdi -
It's obvious you need Step 3 to create bootable media which is the only repair method that doesn't require a password. I give detailed instructions there how to create the bootable media, how to boot it and then the numbered list of repairs to try which now dont' require a password and may work better than the onboard repair mode you already tried.
So please go back and follow the steps I gave, then if you get stuck just ask back and I'll guide you further.
If you have your files backed up you could skip to Option 7 to do the Clean Install which shows you everything that works best in Windows 10 and is such a great learning experience in itself if is worth doing it over. You will get and keep the best possible install to the exact extent you stick with the steps, tools and methods in the linked tutorial.
If you don't have your files backed up it shows how to use the bootable media to do so in Option 8.