You had just did a weekly install of some OS which did not detected Linux, Follow the steps mentioned below to get GRUB working again. Please note this would erase the current bootloader and install a new one for you if you are unsure of what you are doing do not try this
if sudo doesnot works switch to root user and use grub drectly, Find the ROOT device you will get the values for X & Y which will be used later.
Set the root device from the information achieved from the above command
Reboot the system without using the live CD you will dind your boot loader back :)