Restore GRUB

1. Boot from a Live CD (any Linux distribution, doesn't matter)
2. Open a terminal window
3. Type "grub"
4. Type "root (hd0,6)", or whatever your harddisk + boot partition numbers are (pressing tab on the keyboard will auto-complete for you)
5. Type "setup (hd0)"
6. Quit grub by typing "quit".
7. Reboot.