Boot into recovery by holding the command and r keys down while booting. That should bring up the recovery menu. Use Disk Utility to repair the hard drive. If that completes without error, try to reboot normally.
If the repair disk works but the system still won't boot, you can try, from the recovery menu, to reload OS X 10.8. When done, run Software Update several times until there are no more updates.
If that doesn't work, take it into Apple for Service. If your system is <90 days old or you have AppleCare, you should use the Apple support via phone.