I have an external firewire hardrive and after I do not access it for say maybe a day or so the drive letter disappears and I can't access that drive. It does not show in my computer or disk management.
The firewire device has the latest driver and says it is working properly.
If I remove the firewire cable and the power then plug it back in it still does not show up.
If I reboot it will show up again and can be used.