iPod not showing up at all on Mac but works fine on Windows?

I've been searching for an answer on these discussion boards for hours and have not yet found any situation that was quite like mine and I'm getting a bit frazzled and worried.

I have a 120GB iPod classic, which I've used for two years with an ACER laptop and it works perfectly. Two months ago, I switched to a Macbook Pro and synced my iPod with it; again everything worked fine. My iPod was synced with the Mac and all the new music had been transferred.

Today, I've been trying to connect my iPod to my Mac but nothing happens. It only charges (and I can't even be sure that it IS charging because the charging green sign does not show up on the iPod). It does not show up in Finder, or in the iTunes source list; it does not sync. I've reset it a billion times, restarted my mac, switched USB cords and USB ports, even downloaded and installed every software update imaginable but nothing is working.

If I leave the iPod connected to the Mac for a while, something even more alarming happens. It connects for around 3 seconds, and then ejects itself repeatedly. It's like watching someone go insane.

Naturally, I freaked out and tried to connect the iPod to a PC and it is working perfectly on the PC. Please, someone help. I have no idea what's going on.