Currently Being ModeratedAug 11, 2012 4:17 PM (in response to hectorpa)
Boot it in Safe Mode:
1.) Reboot your Mac
2.) After you hear the sound press and hold SHIFT
3.) When you see the grey background and the Apple AND a loading bar underneath it, release the SHIFT
You'll see Safe Mode written in red letters in the top right corner.
After doing this, are you able to open the preferences?