Assuming that you have a USB GPS.... I'm willing to bet that this is a USB Driver issue. I had the same problem with my iPod Shuffle. When I'd first plug it in it would work OK for about 2 min. Then it would disappear. I downloded a patch from Microsoft a couple of months ago that fixed the issue. You may want to start at the Apple support website to see if you can triangulate on the problem that way.
Hope this helps!
Last edited by eherlihy; 06-19-2007 at 04:13 PM.