The Main Menu has the following entries:
*Files
*Database
*Now Playing/Resume Playback
*Settings
*Playlists
*Plugins
*System
The primary ways of starting music playback are either through the file browser (browsing the contents of the HD) or the database (containing metadata scanned from your media files).
It sounds like you are having problems with both methods. Try a file system check first. It's possible that a damaged file system is causing these problems.