Problem with external firewire drive

I am running pro tools 7.4 LE on a duo 2.33 ghz iMac. I have been using a 500 gig Lacie firewire 800 drive as my main audio drive. Yesterday, for no apparent reason, the drive will not boot. It does not show up on the desktop. I have tried switching cables, restarting, using a USB cable and hooking it into my firewire 400 port (I have another hard drive (not a Lacie) hooked up here for backup). Any suggestion on getting the drive to boot (at least one more time...so I can pull all of the files off to another hard drive)....

PK