Well, this was odd. I had been running L4 just fine through yesterday. After hiding unwanted resources my library had 774 resources. I just fired it up today only to discover there were only 2 resources in my library. All the resource files are still on my HD. I had made no changes to my system. This was literally out of the blue.
I was able to remedy the situation, so if this happens to you try rebuilding the database. It's simple.
First, close Logos.
(On XP) Browse to:
C:\Documents and Settings\user\Local Settings\Application Data\Logos4\Data\random-file-name\ResourceManager
(On Vista) Browse to:
C:\Users\user\AppData\Local\Logos4\Data\random-file-name\ResourceManager
Once you're in the the Resource Manager folder, delete the file named "ResourceManager" - it should display as a database file with the yellow cylinder icon.
Next, restart Logos. It should take a few moments to rebuild the database and your resources should be displayed again in your library.
I hope this helps anyone who had a small panic attack.