MBPr Late-2013 sudden keyboard/trackpad freezing

Hi all,

So I recently got my MacBook Pro (13" retina - late 2013) back from an authorised Apple service provider (we don't have real Apple stores in New Zealand), and installed Yosemite shortly thereafter. All they did was replace the screen, it's the same "body" (checked machine ID).

Anyway, I'm suddenly getting this issue where my keyboard and trackpad freeze up, but the system seems to still be going (MenuMeters showing activity, clock running, etc.). The power button seems to be the only one that works.

Have done all updates - it has never done this before!

Cheers,

James