Hi!
Seams I solved my problem with user's posts on this blog. Thank's guys. I noticed that I had a Win 7 Pro N version. So I used the link to Microsoft download that you'll find in this thread. I had to download the Win 10 Pro N version to get a clean update without prompting for a key or S/N.
Now it works. Not perfect, but it's Ok to get a view on the final release of Win 10.
Ciao
Dan :-)