Thanks for the post. I'd like to help! You need to use a VST with your keyboard to output sound from your computer. There are no built in sounds inside your Vortex. The Vortex is a MIDI controller that controls the sounds from your VST. Make sure you're using a VST with your Vortex. Refer to your VST's instructions on how to install the software and use it with your hardware.
Thanks Chris - I'm not expecting any noise to come out of the Vortex (hence why I said "can't get any noise to come out of the PC" - would I be right in presuming that Ableton Live 8 is a VST? It was the disc that came with the MIDI controller - if that's what you're talking about, that's the issue I'm having. I've installed it, I've followed the instructions, no joy.