Some users are finding that their Windows system does not have a MIDI device installed. Microsoft GS Wavetable Synth used to be installed on Windows computers, but if it is not you will need to install a MIDI synthesizer. One we have found is CoolSoft VirtualMIDISynth: http://coolsoft.altervista.org/en/virtualmidisynth
You need to download the file and install. Then scroll down the page to the section Sound Fonts. Select one or more to install and try. If you do not know how to do this, your local computer expert can help.
Next, Set the default MIDI device in BioExplorer. In BioExplorer | Preferences | Audio select the Default MIDI Device.