I apologize for my ignorance but I do not do well with computers and especially Macs. I just got a 24 inch iMac (2008 model) You can turn it on but cannot log in. The screen says "This drive has reported fatal hardware errors to disk utility". And then under that it says "if this drive has not failed completetly back up as much data as you can and replace it with a working drive. What do I do? Will this cost quite a bit to fix? Thanks in advance.