I would give Boot Repair a go which you can find details about here
This as they detail is
Boot-Repair is a 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.
As it looks as if your Ubuntu is at least working I would install it in Ubuntu using the following commands in a terminal (which may look tricksy but it is not really. Open a terminal up (ctrl-alt-t) and type in the following:
sudo add-apt-repository ppa:yannubuntu/boot-repair && sudo apt-get update
sudo apt-get install -y boot-repair && boot-repair
The link above has a guide on how to use but basically it is as follows :
launch Boot-Repair from either :
the dash (Unity)
System->Administration->Boot-Repair menu (Gnome)
by typing 'boot-repair' in a terminal
Then try "Recommended repair" button. When repair is finished, note the URL that appeared on a paper, then reboot and check if you recovered access to your OSs.
Hope that helps
Let us know how you get on.