If you moved your iTunes library to somewhere else other than ~/Music on a Mac or My Music on a Windows system, updating iTunes may have, when unable to find the iTunes folder in the expected location, reset the iTunes' Music folder location back to the default directory. On a Mac, with iTunes closed/quit, launch it with the option key held down, and select the option to choose a library and point it at where you have the iTunes folder located. If on a PC, hold down shift, and launch iTunes, then use the same trick to point it towards the library. Assuming the .itl and .xml files associated with the iTunes Library are intact, you should be able to recover your media files without having to reimport the content back into iTunes.