Why does the Prepare Fake Book command create an empty part?
The Prepare Fake Book Lead Sheet command (in the Part menu) produces a single part with the melody, lyrics, and chord names. This command tries to automatically determine which song track has the melody, and which has the lyrics, before it merges the melody and lyrics together to create a new part. The command might guess the wrong tracks, and it might even incorrectly select as the melody track one that has no notes (some karaoke files are set up with no notes in the lyrics staff/track). In this case, the command will produce a Fake Book Lead Sheet part with no notes.
If this happens, start over. Before you use the Prepare Fake Book Lead Sheet command, play and view the song to determine for yourself which track has the melody. Then specify this track when the Prepare Fake Book Lead Sheet dialog asks you which is the melody track.