Try rocking the handwheel back and forth but don't force it, all you want to do is look for what moves and what doesn't while you're doing it. That will help isolate where it's frozen.
The White I've been tinkering with did pretty much the same thing as your Bernina. The frozen part on the White was the hook assembly was rusted up. As soon as I took it apart the machine turned just fine.
Rodney