Under the preferences of the "Finder" under "general" headings "Show these items on the Desktop" is "External disks" checked or not? If it is unchecked, then naturally the Firewire disk will not appear on the desktop but will appear on the side panel of an open Finder window. If this does not help, then the Firewire plug may be a problem. You do not mention the model of your G5, but there is usually more than one Firewire port. Have you tried an other port? You did not mention if your GTech Drive has a USB port and if so, have you tried connecting via it?