I think the original poster's problem had to do with library filters.   If you are not using any filters, then the folders should all show in the browser.   This could also be the result of changing the folder used to store the library files.  Check your preferences to see where the library files are stored and make sure that you actually have a Core Libraries folder and that it has a bunch of .calib files in it.  If not, then maybe they were moved or maybe they somehow got corrupted. 
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