I HAVE THE SOLUTION!
Go to Control Panel/System and Security/Action Center
There is a title: "Review recent messages and resolve problems"
Under that I had three warnings. Than I turned everything on.
After that I was able to install .net 3.5 without the 0x800f0922 error code.
Use the
Control Panel | Programs and Features | Turn Windows features on or off.
solution.
I hope it works for everyone with this.