Cannot boot to Ubuntu, though installation was successful

I installed Ubuntu 12.04 on an HP Pavilion H8-1228 computer via USB flash drive. Installation was a success. My computer still starts Windows, but there is no way to boot to Ubuntu.

I tried hitting F5 to display a boot menu. There is no "Ubuntu" option.

How can I boot into newly my installed Ubuntu system?

Usually when this happens it is because Ubuntu's installer didn't properly install the boot loader.

Assuming you installed Ubuntu by booting from a live CD/DVD or USB flash drive (or from the alternate CD) and running the installer (that is, not from within Windows using Wubi), you can fix this problem by reinstalling GRUB2 to the Master Boot Record using one of these methods.

Seems like your boot loader is missing from your primary boot drive, or just doesn't contain any reference to your Ubuntu installation.

When I face this type of issues, I use on of this two applications to salvage the situation:

• Super GRUB2 Disk

  The primary purpose of Super GRUB2 Disk is to help you boot into an OS whose bootloader is broken.

• Boot-Repair

  simple tool to repair frequent boot issues you may encounter in Ubuntu like when you can't boot Ubuntu after installing Windows or another Linux distribution, or when you can't boot Windows after installing Ubuntu, or when GRUB is not displayed anymore, some upgrade breaks GRUB, etc.

insert ubuntu cd and select try ubuntu, connect to internet opne terminal ( Ctrl+Alt+T ), login as root:

sudo -i

find out your linux disk :

fdisk -l

mount it:

mount /dev/sdaX /mnt

Recover:

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