grub2 - After installing Ubuntu 12.04 pc goes in GRUB rescue

As a part of my school lab I did following:

• Starting off with win 7 installed


• Installed 10.04 in remaining space > worked


• Installed 12.04 in amother partition I created finished installation took out the disk.

After the 12.04 the system booted into Grub rescue mode.
I didnt know what to do as I never used ubuntu so I just moved on to install 14.04 as part of lab hoping the previous grub loader problem will be solved then, by replacing Grub from CD.

After the 14.04 installation I still get the Grub resuce prompt.