Sometimes GRUB stops working out of the blue. Other times, Windows kills GRUB out of spite – when you install Windows, GRUB breaks. One way to fix GRUB is via the command line by using a live CD. An easier method is Super Grub Disk.
At the Super Grub Disk menu keep pressing enter until you get to an option screen that lets you choose Linux or Windows. If you have recently installed Windows choose Linux and then reinstall Grub. The process is automatic. After that reboot and remove the disk. Grub should now be working. Play around with Super Grub Disk and learn how Grub works.
If Super Grub Disk does not work check to see if your Hard drive (HD) is plugged in correctly. If you have two hard drive switch the IDE cables. This might solve the problem.