If you have a Mac Pro with an upgraded NVIDIA Quadro 400 graphics card, upgrading to Mac OS X 10.6.7 may cause a wide variety of problems, ranging from video artifacts to no video at all. The fix is to apply the latest standalone driver update from NVIDIA’s website, currently version 256.01.00f03v7. If you are experiencing no video after updating a Mac Pro with a NVIDIA Quadro 400 graphics card to Mac OS X 10.6.7, you’ll need to temporarily install a different video card to download and apply the standalone driver.