I have a 2009 iMac with Yosemite installed. My external firewire drive shows up in the system report as a 2 Terrabyte drive in the firewire bus, but will not appear on the desktop and can't be used by final cut. It does not appear under "storage" in the system report either. This happened tonight, after months of use. I tried shutting down and restarting everything and can't make it come back. What next?