Try booting in Safe Mode without using Terminal commands.
http://support.apple.com/kb/HT1455
Have you tried booting from your install disk?
Insert the installer disk and Restart, holding down the "C" key until grey Apple appears.
Go to Installer menu (Panther and earlier) or Utilities menu (Tiger and later) and launch Disk Utility.
Select your HDD (manufacturer ID) in the left panel.
Select First Aid in the Main panel.
*(Check S.M.A.R.T Status of HDD at the bottom of right panel. It should say: Verified)*
Click Repair Disk on the bottom right.
If DU reports disk does not need repairs quit DU and restart.
If DU reports errors Repair again and again until DU reports disk is repaired.
When you are finished with DU, from the Menu Bar, select Utilities/Startup Manager.
Select your start up disk and click Restart
Carolyn 🙂