I have had this happen to a laptop much worse than a desktop.

Nightmare's Solution is right on try using a live linux disc, there are many flavors. They boot linux off your cd-rom and let you run the linux os off the disk. You can access all your files on your hard drive. You will need something to transfer them onto another hard disk or a flash drive. That's your best bet. DistroWatch has Tons of linux variants, linux mint is really simple to use good luck,