I have updated adobe lightroom to the new 5.7. Today, I imported 133 photos from my compact flash. It imported them all as normal and then turned them all black?! I removed them, rebooted, and started over and the SAME thing happened. I can see all 1600 of my previous photos. I can see the photos in the catalog on my hard drive. I can see them in iPhoto. I just CANNOT see them in lightroom. WHAT IN THE WORLD IS HAPPENING? THEY ARE RAW CR2 FILES. HELP!!!
Turn off auto-tone on import. It is in Preferences->Presets. Some versions of Lightroom have a bug that when you have that enabled it will turn your pictures black because it applies a -5.0 EV exposure compensation. For already imported pictures, just reset their develop settings and they will be normal again.