Have recently bought an (early 2012) iMac 27'' with wireless keyboard which is not responding anymore. Computer is trying to find it, batteries are new & working (green light keeps flickering) but the keyboard doesn't connect anymore. Went to the shop and got a brand new wireless keyboard, but same problem. Where do I stand? Can this be a problem with the actual desktop? How long is it going to take to get this sorted - I have a lot of work to do and no back-up machine.