Keyboard not detected

System: Windows XP Home Ed. sp2

MuseScore seems to be working fine, except that I can't input notes using the piano keyboard. On the MuseScore preferences page, under the IO tab:

Use midi output is blank (not ticked) -- and is not selectable
Use internal synthesizer is ticked.
JACK Audio server is not ticked -- and is not selectable
ALSA Audio is not ticked -- and is not selectable

Portaudio is ticked and the boxes read Api: MME Device: Microsoft Sound Mapper - Output

Un-ticking the "Use internal synthesizer" box does not cause any of the others to become selectable.

I've connected my keyboard to my pc using a MIDI to USB lead.

I've tried Opening Musescore with the keyboard switched off, or already switched on - makes no difference.

Do I need to set up the JACK audio server? From the instructions that appears to be necessary only if I'm on Linux. If I do need to set it up, then where is it? The instructions just say "Open the "JACK Audio Connection Kit", with no indication of where it's to be found.

This is my first attempt at connecting a MIDI instrument to a computer, so it's quite possibly I just don't know about some vital step that's "obvious" when you know!

Thanks for your time.

PM