In olden days, when horses sh@t in the streets and real men wore spats, computers came with a game port. (for joy sticks etc). this could also be configured for midi in-out.
I think you're mistake about the 12 Volts, though as I believe they only offer 5. You can find a pin-out here:
http://en.wikipedia.org/wiki/Game_port
MS discontinued support for the game port (either in XP or in Vista - I can't remember).
The standard way of controlling midi nowadays is via USB, and there is quite a large choice of USB midi keyboards out there. Maybe time to replace the keyboard?