There is very little to the hardware for midi-in, just an opto-coupler, a few passive components and IC49/55, which then feed directly into the CPU
You may want to re-seat the opto coupler (every one I've seen has been socketed) and if you can check pins 12 and 13 of IC55 you should see them pulsing when midi data is being received
I'm guessing this is a configuration issue (not easy given the instructions in the manual!), it might also be worth upgrading to the newest and most stable version of software