I've had Ubuntu 12.10 running smoothly for over three months now, but today it go stuck on the login screen and wouldn't recognise any keyboard or mouse actions.

I forced it to shutdown and turned it back on again, but now am greeting with a simple terminal screen saying:

error: attempt to read or write outside of disk 'hd0'.
grub rescue>
Anybody got any ideas what's causing the issue or how to solve it? Any help is much appreciated.