Both FB 4.5 an 4.6 are no longer loading. I've read the solution that suggests that you need to delete some of the hidden files and relaunch - and it doesn't work. I've trashed the preferences and searched everywhere possible for an answer.
It happened a month or so ago that 4.5 had this problem, so I downloaded and installed 4.6. now both files are not working.
The worst part is that when I installed 4.6, it uninstalled most of my (legitimately licensed) CS5 applications and Adobe support said they couldn't help me recover them.