Trying to record a song from the keyboard onto a disk but it does not have anything on the disk.

When saving a song onto the disk, you should specify which format to save it in SMF, etc. Once saved to disk, it will need to be re-loaded back onto the kyboard in order to play the song back. Make sure that the identical format is chosen when reloading the file from the Disk back onto the keyboard. If a different format is chosen, it will not find the file.

On the WK-1800 this information is found on page E-67 of the Users Guide.