If I understand correctly, calibre is crashing (or shutting down) as soon as you click on "Load plugin from file," right?
Do you happen to know what the location of the folder is that the "Load plugin from file" dialog is trying to open? Perhaps you can see it in the brief glimpse you get before everything disappears? Or you remember that last folder it opened to before it started misbehaving? Or perhaps you recognize some of the files in that quick glimpse?
What I'm getting at is that I've had rare situations where calibre barfed when file/folder dialog windows were trying to view the contents of a folder that had a corrupt file in it. The problem is that the "last folder opened" is remembered by calibre (and those settings will survive a normal uninstall/reinstall) and it keeps trying to open that same folder that's going to make it barf. So if there's any way you can figure out which folder the "Load plugin from file" dialog is trying open, you could try browsing to that folder outside of calibre and moving/copying/deleting everything out of that folder so that it's empty when calibre tries to open it. You may find that many apps (not only calibre) barf when trying to open that particular folder. Get that folder located and the underlying problem fixed and your ability to load plugins from files should be restored.
Last edited by DiapDealer; 02-23-2013 at 08:33 PM.