musescore not recognising my MIDI keyboard

Hi. I'm trying to connect my Casio CT-500 keyboard via MIDI to musescore, but even though I seem to be following the correct sequenced steps (turn on computer but don't open MuseScore yet, connect keyboard, turn on keyboard, open MuseScore, make sure 'enable MIDI input' is checked ON) when I go into edit-preferences-Audio&MIDI, MuseScore doesn't recognise my keyboard, i.e. I can't select it in MIDI input or output (because it doesn;t show up). Can anyone help? Thanks!