1) Does the system profiler see it?
2) do other computers see it?
3) does your machine see other Firewire devices alright?
If the answer to 1) and 2) is no, and the answer to 3) is yes, then your hard drive is broken.
What is it, though - a LaCie, or a Western Digital (LaCie generally doesn't indicate what brand drive they're using in their Firewire enclosures).