This is probably a noob question or I am just beeing stupid (wouldn't be the first time ... ).
When I select something in the object window and click Preview, nothing happens. The "Open Windows" thing says that the preview window is open.
I already thought that it was just "offscreen" somewhere so I changed the display resolution, and looked carefully around the edges of the screen, but it doesn't look like it is there.
I just got this computer a few months ago and reinstalled all the things ( Skyrim, CK, Steam ...) and this is the first time that I am using the CK on this computer.
On my other computer (crappy laptop that could barely run Skyrim on lowest settings) everything worked fine ....
I also have Fallout 4 installed and the Creation Kit for that game works fine, including the preview window.
So I don't think it's the fault of the computer itself.
If anybody knows a solution for this weird problem, let me know!