Booting problem after installation

[d.davolio at mastertraining.it]

Hi everybody,
I'm planning to use a nice server to implement an Edubuntu 12.04LTS 
School lab.
I installed from USB on a dual processor server with a Raid 10 storage. 
Since the storage is like 4 terabyte and Edubuntu see only one large 
disk /dev/sda, I let the installer do the automatic partitioning and 
installation. After the installation the server booted correctly, then I 
installed the upgrades (Update Manager).
After that, the server doesn't boot anymore and stops at the "grub>" prompt.
I'm still able to boot giving at the grub> prompt the linux and initrd 
right commands but even after boot, an update-grub and reboot, the 
server stops at grub>.
Here some detail: the installer used the GPT table and I have 3 
partitions, /dev/sda1 (bios_grub), /dev/sda2 (root filesystem) and swap.

Is there any known problem with this configuration in Edubuntu as far as 
you know?
Thanks for the help!
Davo