So, I have this two year old 320GB toshiba external HD. It works with a USB cable. When I plug it into my MBP (from 2009) it works. When I plug it into my MacBook from 2007, the light on it comes on but I cant' mount it. I've opened Disc Utility and I dont ever see it there. How can I fix this? Any thoughts? I have used other portable external HD's on that MacBook so I'm not sure how to solve this problem.