I use Lightroom with Creative Cloud (Windows 7, 64-bit), and this evening has a problem starting starting the application.
The Creative Cloud app indicated that the Creative Cloud Libraries failed to install, so I followed the online advice - remove and reinstall the libraries. That succeeded.
Lightroom 5.5 failed to start again, same symptom: splash screen and window open, but the app hangs.
Creative Cloud showed LR as "up to date" but not installed. So installed, and now got Error 5 on starting Lightroom.
I uninstalled and reinstalled, but I see the same error.
Keith's reply did not reveal the answer - just a number of error 5 complaints with 0 replies.
Here's how it worked out:
A day later, I tried running LR again. Still saw error 5, but when I dismissed the dialog, LR opened to a new error, the well-known "Develop module disabled."