If it is still under warranty try calling Applecare first. If that doesn't help, back up the computer and either take it in for repair or try reinstalling the system. Best wishes.
I think it means there is something wrong with the filesystem-not the actual, physical HD. Repair (you need to boot from the OS X Install Disk 1), and fsck if needed. Repair permissions, and you should be fine!
restart the machine, and hold down the Apple key and the letter S. This will boot into single-user mode.
you should see a black screen, with a cursor. At the cursor, type this exactly as shown fsck -yf
hit return
that'll run fsck. If it returns an error, just run it again. Keep running it until no more errors are reported. When there are no more errors, type in shutdown -r now
hit return
that'll reboot the machine. Try this and see if it helps.