Reinstall Grub boot loader After installing windows

http://www.howtogeek.com/howto/ubuntu/reinstall-ubuntu-grub-bootloader-after-windows-wipes-it-out/

1) Boot off the LiveCD
2) Open a Terminal and type in the following commands
    sudo grub
   root (hd0,0)
   setup (hd0)
   exit

Reboot (removing the livecd), and your boot menu should be back.