I have a iMac G4 800Mhz running 10.4.9 and I just purchased a WD MyBook Pro 250GB for it. I hooked the drive up on Monday via FireWire 400 and it worked great. I woke up the next morning and my iMac won't recognize it via FireWire 400 anymore. Yes I have checked disk utility and system profiler and it does not show up at all. It works via USB, but my iMac is USB 1.1. Of course that is too slow. I called WD Tech Support and they figued out the obvious for me, that either the Firewire ports were bad on the drive or the iMac. I hookep up the HD to my fiance's MacBook G4 1.25GHz running 10.4.8 via FireWire 400 and it recognized it. At this point, I was pretty convinced that both FireWire ports on the iMac were toast and took it up to the Apple Store to get it looked at. An Apple Genius hookep up a flash drive to the firewire poirts and it was recognized. At this point, I am not sure what to do except for take the drive back and never use a WD product ever again. Their support was horrible. Could it be a driver issue? Any help would be greatly appreciated. Thanks.