Thank you for reporting this bug, I'm sorry that you have troubles. Please forgive the late reply. I was on the road without any internet access.
I downloaded the program from the Appstore today to try.
I suppose you downloaded the lite version, am I right?
When I start the program thumb pictures are not loaded (spinning wheel forever).
Do you mean the OS X spinning wheel or Coollector's spinning wheel that shows that a picture is downloading?
When I try to do anything, nothing happens. In the dock the only choice I have is Force Quit.
That's strange... The program has never worked, not even for a short time?
Could you please try the version from MacUpdate.com to see if you have the same issue:http://www.macupdate.com/app/mac/40674/coollector-movie-database
I'm running Mavericks on a Mac mini late 2012.
There's no known problem with Mavericks. It should have worked.