I have one more suggestion. With the Snow Leopard (system) cd in the cd drive start the machine but just as you turn it on hold down the "c" key. This will boot OSX using the cd instead of the hard drive.
If the machine boots (it will take about 6 minutes) try to navigate to your hard drive and try to find that school work you don't want to lose. You can try to copy it off of your machine with a flash drive that you plug into the usb port...
If the machine doesn't boot when using the Snow Leopard cd then you are probably going to have to take it into apple. Tell them about your school work and ask if they can recover it for you...
One more point...
If you asked me for help and you lived next door....
I would open up your machine, remove your hard drive, put it in my external enclosure, attach it to my mac and see if the problem is your hard drive. We could also try to get your school work off of the disk.
Doing the above would tell us if your hard drive was bad or if the rest of the machine had the problem.