Once Mac OSX Lion starts booting up, you may press the following key combinations for analyzing and/or fixing your system:
- Command + V => Verbose mode, so you can check what makes your system wait or which error makes it stuck.
- Command + R => Recovery mode, you can access disk utilities to check and/or fix your disk, access the Internet for solution, and reinstall your OSX.
- Option => You can select which disk to boot
- Command + S => Single user mode, the system will boot into terminal mode and login as root. You can also try to check and fix your disk here, via commands (fsck, fsck_hfs etc.)
- C => Boot CD/DVD rom.