Windows 7 and Ubuntu 13.04 dual boot, GRUB menu not showing

Boot up a live usb and try to repair the bootloader with these commands:

sudo add-apt-repository ppa:yannubuntu/boot-repair

sudo apt-get update

sudo apt-get install boot-repair

After installing 'boot-repair' launch this program from dash by searching for the term and click its icon to launch it.

If this doesn't work then boot into Windows 7, download and install a freeware called 'EasyBCD' (latest version is 2.2)

After installing this tool, select 'add new entry' column and install grub under the Linux tab.

Sorry I'm on my phone now so I can't add links and pictures to the post. I'll surely edit this post today when I get to the house

Hope this helps.