Hi
Like what Lokasenna said, you have to assign instrument to your MIDI notes.
But you can use General MIDI instrument to preview what your MIDI sounds like.
if you are happy with the Notes you can download better instruments.
http://www.vst4free.com/
To use General MIDI
Goto Preferences > MIDI Devices >
In MIDI output section Enable Microsoft GS Wavetable synth
In tracks:
click on Route button ,in MIDI Hardware output select Microsoft GS Wavetable
click on FX button , add Cockos > Reacontrol-MIDI effect.
In Reacontrol:
Enable Bank/Program select
click on load file and choose GM.reabank
select bank General MIDI
