Apple loops and sound effects not showing in FCP X 10.1

Trash the FCP X preferences and restart FCP X

Download the free Preference Manager

Delete the preferences manually

• User > Library > Preferences > com.apple.FinalCut.plist and
• User > Library > Preferences > com.apple.FinalCut.LSSharedFileList.plist

if you cannot see the Library in the user home folder

• Open user home folder by <command><shift><H>
• Click 'View'
• Select 'Show View Options'
• Check 'Show Library Folder'

or

• from Desktop, click "Go" with <Option> key, select Library