A partir deste link: link
4) Re-install GRUB
Now you have windows 7 but it has completely eaten your boot loader so you need to re-install grub. Boot from the ubuntu live cd and go to terminal. Type in terminal:
sudo grub grub> find /boot/grub/stage1
That should return your Ubuntu partition in the form of (hdX,Y), use that:
grub> root (hdX,Y) grub> setup (hd0) grub> quit