whenever I plug my iPod into the dock, it lights up for a second, then starts charging, but almost never shows up on the desktop or in iTunes. I then have to disconnect it "without" ejecting it. Sometimes if I unplug the dock from the firewire port on the back of my iMac wait a few seconds then plug it back in, then plug my iPod back into the dock, it works, other times it doesn't. Any suggestions?