Ableton Push not showing in Audio MIDI Setup

Hello - I hope that somebody can help.

I've plugged my Ableton Push into a USB port on my Mac Pro which runs Yosemite 10.10. It's not showing up in Audio MIDI Setup. Even when use the + button and add Push manually it still doesn't work. Push just sits there saying please start Live. I've tried uninstalling all other MIDI drivers and rescanning MIDI but still no Push. I've tried the Push on a USB for an old Windows laptop with Live and it seems to work on that so it's Apple configuration rather than anything else. Also I tried a clean install of Yosemite with a demo version of Ableton and that seemed to work but when I went back to my full licence on the main Yosemite partition it stopped working again.

Thanks