Well you can try rebooting and holding down Command Option P key and R key all at the same time after the tone. Keep them held down until you hear the start up sound again. You just zapped the Pram, which might get you back rebooting.
If not, reboot again.
1. Restart the computer holding down both the Command key and the S key.
2. After lots of text appears on the screen, type "fsck -y" (no quotes) and hit return.
3. The system will write some messages on the screen. If it says that the volume was fixed or changed, redo step #2.
4. When you get the message that the system is OK, you can either type "halt" to shut it down completely, or "reboot" to start it back up again. shutdown -n now