Cannot format an external Firewire disk

Hello.

I've been using it for more than three years. Today I got strange behavior navigating on it.
I went to disk utility to Repair -> Cannot unmount the disk

I Force Unmount it and repeated Repair -> Cannot repair, format

I have a backup so I don`t care to format it.
Format -> Unable to write to the last block of the device

I turned it off and on again, it is recognized and mounted. I can see folders but all of them Zero Items.

As I said, it cannot be ejected -> The disk “LaCie Firewire” wasn’t ejected because one or more programs may be using it.
Force unmount has to be selected.
I also restarted the computer, OS 10.8.4 but no changes on error messages.

Thanks for help