My 27" mid 2010 iMac needed to come apart as the Bluetooth wasn't working, the machine was an eBay refurb whereby the seller had replaced the screen. I thought while I had it open I'd replace the i3 3.2Ghz with a 2.8Ghz Quad Core i5 760. The i5 just wouldn't boot at all and so I put the i3 back in and "fixed" the bluetooth (the antenna cable hadn't been connected). I've taken plenty of iMacs apart before so I know to be careful and take my time however this time something has gone wrong, I've lost audio. The machine still makes it's chime through the inbuilt speakers and the digital output is still recognised in system preferences but the headphone/speaker output is dead and my volume controls are grayed out/show the stop symbol. I've tried the usual, OS X re-install, NVRAM Reset, SMC reset, headphones in and out of the socket, but no dice. Anyone have any idea why this might have happened? The speakers are working which is evident from the chime so I'm 99% certain everything internally is connected, I know the input ports are connected directly to the logic board so not much to go wrong there either. Also, anyone know why the i5 760 wouldn't boot when people seem to have so much success with the i7-870?