Someone I teach has just rung me today with exactly the same problem, although their OS is Win 98SE. If it is plugged in to the Front USB port the computer reboots, but it doesn't reboot if it is plugged in to an external USB hub. Unfortunately, I won't be seeing him until next Wednesday. If I solve the problem I will let you know. In the meantime I will keep checking this thread to see if someone else comes up with the answer before me.