I can't access the system: Error: "unknown filesystem. grub rescue"

I can't access the system: Error: "unknown filesystem. grub rescue"

i'm a fresh ubuntu user and I've installed a double boot with Wind 8 and
Ubuntu 13.04, but since yesterday I'm receiving an error showing:
error: unknown filesystem grub rescue>
The fact is when I do ls (hdX,gptY)/ all I get is "error:unknown
filesystem" again.
And the solutions posted don't work because I don't know why but I can't
access the BIOS pressin F2 or to the boot pressing F12, the simply don't
work since the error.