I suspected something like this happened.
You had Vista installed on the first partition. You tried to install Ubuntu and created a second partition. That failed. You tried again and created a third partition in the process. That succeeded. Now grub expects to find Ubuntu in the third partition.
Then yuo deleted the second partition (the failed install). Now Ubuntu is in the second partition, and grub is looking for it in a non-existing third partition.
In your grub configuration file which is located in /boot/grub, the config shows grub in (hd0,3 for grub 2) and in (hd0,2 for the legacy grub installation).
Boot your Ubuntu install cd as a liveCD, Mount the Ubuntu partition and edit that config file to reduce the hd0,X number by 1.
Grub should work then.