What happened to my imported music? I have no idea what I'm doing wrong ... or what iTunes is doing wrong ... but when I go into my Library, the only music that shows up is the stuff I actually purchased from iTunes.  Over the years my husband and I have gradually imported pretty much our entire CD collection ... but suddenly NONE of that is accessible.  Where did it go?  How do I access it?  It's like iTunes suddenly broke.  I can't update any of my playlists, because the music no longer exists.  I'm so frustrated I could just cry!
While iTunes is open, click the menu: iTunes > Preferences.
Click the Advanced (gear) icon.
Look at the "iTunes Media folder location." Is that where your files are located? You can click the Change button to point at the correct location (which is generally, as someone already commented, in your user folder > Music > iTunes > iTunes Media > Music).