Why not use iTunes to restore the iPod to its factory settings, then re-synch it ?
EDIT - I myself did suffer the same problem with my Classic - the tracks all disappeared, although the space was still being used. iTunes could not repair the iPod, giving some meaningless error code. So out of desperation I went into "My Computer", right clicked on the icon for the iPod ( it shows up as a drive ) and selected "Format". This left me with a blank iPod. When I relaunched iTunes it detected the corrupt iPod once again, but successfully repaired it. I then clicked "Sync", and all my tracks were loaded back into the iPod. Took ages to do, but it worked . . . .