1: Please post on “Cubase 5 and 4” sub-forum.
2: Please be more accurate on your description: “no sound response from Cubase when touching keys” can mean anything depending on what is this “sound” you are excepting to hear. Virtual Instrument? Sound of your hardware synth routed through Cubase? If hardware synth, in which way it was routed? If virtual instrument triggered with MIDI, which instrument? Which MIDI driver? etc etc etc.