I have a 2007 mac pro, 2x dual core xeon, lion 10.7, NVIDIA GeForce 7300 GT 256MB, 24gb ram, 250gb ssd, 3tb sata hdd. I have had no audio now for a few weeks, it first happened when I tried updating my graphics card to a gtx 560 graphics card, so I thought this was the problem, so I downgraded back to the GeForce 7300 GT and reinstalled lion 10.7, (before that I had updated to 10.7.5, many people also complained about no audio with this update), so I reinstalled lion to 10.7 hoping this might fix it, but it doesn't. I have reinstalled to factory settings, resetted pram settings, resetting smc settings, tried booting in safe mode, I have repaired disk permissions, I have verified disk permissions, on all disks. I don't know what else to do. headphones dont work, built in audio doesnt work, external speakers don't work. my computer works fine in every other way, but the audio won't work. Has anyone got any ideas?