Grub 2 typically gets overridden when you install Windows or another Operating System. To make Ubuntu control the boot process, you need Reinstall (Repair/Restore) Grub using a Ubuntu Live CD.
Ubuntu 12.04 was released on the 26th of April 2012, which just so happened to be a Thursday. From there on in, Ubuntu 12.04 Precise Pangolin provided millions of users all over the world with a free, stable, secure operating system.
Ubuntu 13.10 was released on the 17th of October 2013. This newer version of Ubuntu replaces 13.04 as the latest release, and is available alongside the LTS release, Ubuntu 12.04 Precise Pangolin.