If an application doesn't open anymore or seems blocked on a message that reads "Caching Fonts," you have probably removed the fonts cache.
In this case, don't force the application to quit; wait for the fonts cache to rebuild.
Indeed, the rebuilding of fonts caches in some open source applications (GIMP, VLC, MPlayer OSX Extended, and so on) takes a particularly long time.
After the cache is rebuilt, the application will open again normally.