thought i might ask professionals about it.
I've got a G5 and 2 spare drives, one is a Lacie and the other a MyBook. The problem I'm experiencing is, that neither of them mount when connected via firewire (both 400 and 800). They only mount via USB cable. It's the first time it happend, so far I've been working of them via firewire 800 with no issues whatsoever.
You might have a firewire bus problem. Try resetting the PMU button on your Mac's motherboard. It's a tiny round button usually near the battery on the board. Unplug the power cable first, then use a pencil eraser to push the button one time. Wait 30 seconds then reboot the mac.
What this does is reset all of the power management system wide, resets the PRAM... won't hurt a thing, but I've seen this fix problems like yours many times.
Apple Certified Trainer
Author: "Jerry Hofmann on Final Cut Pro 4" Click here
8-Core 3.0 Intel Mac Pro, Dual 2 gig G5, AJA Kona SD, AJA Kona 2, Huge Systems Array UL3D, AJA Io HD, 17" MBP, Matrox MXO, CD's