I'm trying to install Ubuntu 13.04 on Lenovo ThinkCenter with installed windows 7 from live CD. Everything seems ok but after first reboot from Ubuntu Grub doesn't appears and instead only windows 7 is loading. What can be wrong?

Thanks!

UPDATE:
As Srivatsa Kanchi sad I just had repair grub with following commands:

sudo fdisk -l

It's give me list of partions where I should select with Linux and mount with:

sudo mount /dev/sda4 /mnt

Where sda4 my Ubuntu partition. Next fix grub:

sudo grub-install --root-directory=/mnt /dev/sda

That's all. Thanks!