Okay, so, I pick up my keyboard, navigate through the menus, pick a song, start playing...and the keys won't respond. I restart, nothing. I back out, pick another song, nothing. "Is my keyboard broken?" No, I just pull out my ION drum set plugged into the USB socket and everything works fine.
Was Harmonix trying to make some sort of musical-political statement about how drummers and keyboardists cannot work together? Because that's completely untrue.
Also, sorry if this is a known issue.