When I open Lightroom I have hundred of folders. They all displayed in alphabetical order but when I scroll down to "T" any of those folders from then on I can't click on. They are all visibly there but I might as well be clicking on a blank space as nothing happens. I have tried to optimize the catalog, I've updated to the latest version, and I've restarted my computer. It still won't let me click on anything past the letter T. Any ideas?
Lightroom version: 5.7.1 
Operating system: Windows 7 Business Edition
Version: 6.1 
Application architecture: x64
The one thing I would try is deleting your preference file.
If that doesn't work, I believe this is an old bug in Windows that limits the number items in a scroll list to about 1600.
If you've got that many folders, the only real choice that I know of is to organize these folders in some sort of hierarchy, and then close the parts of the hierarchy taht you're not looking in so now the list is much smaller than 1600 items.
Whoah. That worked. The second bit. What a silly glitch. Thanks!