Currently Being ModeratedDec 13, 2012 8:41 AM (in response to sro37)
Insert your original install dsc and start the computer while holding the C key down. Select your language and at the next screen from the Utilities menu select Disk Utility. Select your hard drive and first check the S.M.A.R.T status. Then select the repair option. It's possible that your hard drive has failed, hopefully you have a back up or you might lose everything. Let's hope for the best.