depending on your material, Melodyne's audio-to-MIDI feature won't work right out of the box. Very likely you will have to tweak the note detection first. See this video
for details. Remember that Melodyne will only export MIDI notes that are also available as blobs. So if you don't see blobs for all the notes that you can hear in the audio, then your MIDI file will obviously be incomplete as well. A correct note assignment is therefore crucial.