Original post by: Rishi Viner ,
If you have been inside the Mac Mini for any reason, then there is the possibility that the ZIF cable from the audio board is not properly seated. If this is the case, you get the exact same symptoms you have described. To quote GaryObrien: "Steps 7 and 8 in the Audio Board install (Installing Mac mini Model A1176 Audio Board) are where the solution lies. There is a painted line on the ZIF cable. Before you close the cable lock, make sure the cable is fully inserted - the painted line will be about 1mm above and parallel to the top of the socket. Push down the clip and all should be well."