Thank you for all your suggestions. Nothing I tried made a difference, so I contacted the tech, and got this back just now: "It sounds as though your computer is for some reason unable to provide the Saffire LE with the power it requires when it is booting up, and as a result is shutting the computer down. The easiest way to get around this is to purchase a 6-to-4-pin adaptor and a 4-to-6- pin FireWire cable, severing the power connection between your Mac and the Saffire LE. The disadvantage of this is that you will need to use the PSU with your Saffire LE. If you would like to investigate further, it would be worth trying your Saffire LE on another computer (with a 6-pin FireWire port) and seeing if you get the same problem." I tried it with another computer and it was fine, so I'll try the adaptors next. I have no idea what would cause my G4 to suddenly not have enough power for the audio interface. Does anyone know why this could be? Thanks very much for your insights.