I am having problem getting my 500GB Western Digital external HD to work. The green lights on the HD are on, and the drive appears in the Disk Utility. I tried to "Repair Disk" but it did not work. It is only USB 2.0 and not a firewire drive. This is would be the first time I have used it since the Leopard upgrade (Archive and Install), but it did not work. Any tips or hints as to what I can do to get this working?