Just today, I plugged in my iPod Classic (bought recently; 160 GB), and it doesn't charge or show up in iTunes. Its screen turns on though.
I have OS X 10.8.5, and the latest iTunes on a MacPro 2008.
I can plug it into my wife's iMac (2011) using the same cable and it seems to work fine.
So I reset the SMC, and the PRAM. I reinstalled iTunes twice, and restarted the mac. The only thing that changed was immediately after resetting the SMC, plugging in the iPod had it show up as connected on its screen for a few seconds, then it said "OK to disconnect" and now doesn't respond any more. I also tried plugging it into the other USB ports, including the ones on the Apple Keyboard.
It looks like the problem is that the Apple Mobile Device Service doesn't start up. I can find Apple's support article on how to reinstall it on 10.6.8 and lower, but that doesn't help. It includes deleting iTunes.app and reinstalling it; 10.8 say you can't do that since iTunes is needed by OS X.
So: how do I get the AMDS working again?