The hard drive may not be dead. Â It may simply be corrupted firmware, which should be fixed by booting into emergency disk mode, then doing a "restore" in iTunes.
It could also be that the hard drive isn't connected properly. Â If you open it up and fiddle around with it (just unplug/plug it, etc, maybe shake it gently if you've exhausted everything else, as the read head may be stuck) it may start working again.
There are videos on taking apart iPods over
here, it's really quite easy.