If it won't even boot up from the disks than its probably something more serious than the hard disk going.
If you can try booting the 'hardware check' disk that came with it.
Regardless of the result of this check, I recommend taking back to apple.
Hopefully you have had it for less than a year and it is still covered under warranty. (especially if you have applecare, give them a call, they might come and pick it up from you.)