OK, let's try this instead:
Boot the machine into single user mode: Reboot and hold down the command and S keys. The machine should boot up to a black screen with white text. If you can get that far, do this: (This has been copied from the Apple KB)
Start up your computer in single-user mode to reach the command line.
At the command-line prompt type:
/sbin/fsck -fy
Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:
** The volume (name_of_volume) appears to be OK
If fsck found issues and has altered, repaired, or fixed anything, it will display this message:
***** FILE SYSTEM WAS MODIFIED *****
Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
When fsck reports that your volume is OK, type
reboot at the prompt and then press Return.
Your computer should start up normally and allow you to log in.
Follow the above directions and let us know.