If you try to play a MIDI file with a media player such as Quicktime or Windows Media Player, or a notation software such as Sibelius, but you can’t hear any sound, the most common cause is that you have not correctly set up MIDI playback.
First of all check that your computer speakers, MIDI keyboard or other playback equipment are plugged in, switched on and have the volume turned up.
Go to Start, Control Panel and double click Sounds and Audio Devices. Click the Audio tab at the top then click the Volume button. There, make sure the main Volume and MIDISynth/SWsynth are not muted and turned up.
Go to the Apple menu, System Preferences. Click Sound and then click on the Output tab. Make sure the Output volume is turned up and ‘Mute’ is unticked.