I tried several methods to install windows 10 successfully. In all cases I unplugged my SSD with Windows 7 Pro on it to protect a working OS. I prepared a HDD by simply deleting the whole disc...

As you have Windows 10 on a HDD, why not clone this to the SSD, as long as you have the space, if not, trim off the HDD what you don't need until it fits.
I did exactly that using AOMEI Partition...