I did something silly. I replaced the trackpad in my MacBook Pro 15" mid-2012. It (for some reason) involved taking the motherboard out (via iFixIt's instructions). Everything works now, except the sound.
OS X reports no input or output devices. Nothing works, even when I plug headphones in. I'm not sure how OS X detects that a sound device is actually recognised, so I can't really troubleshoot the hardware. Any ideas?
I've tried all the usual, reset PRAM, SMC, etc.