strange issues with 5g

I have a PC and my ipod is formatted for windows. The past couple of days I had been listening to music on iTunes through my iPod on a mac. Yesterday I did this and then disconnected it and listened to it in my car just fine. Today when I disconnected it from the Mac and went to listen to it all my music and videos were gone but photos were still there!

I plugged it back into the Mac to see if my files maybe ended up in the trash bin when I dragged it there to eject it, they weren't, however when I opened iTunes on that Mac it recognized my iPod and all my stuff was still there! I once again disconnected it (this time ejected it through iTunes) and my music still wasn't there on the iPod.

When I got home and connected it to my PC to see what it would do and it won't recognize it at all. I get the "One of the USB devices attached to this computer has malfunctioned, and Windows does not recognize it." message. It's almost like it somehow got formatted for a Mac even though I didn't tell it to do so and yesterday things worked fine after using it on the Mac. Also, the Mac seems to think it's still formatted for windows b/c in iTunes where the option to update the iPod is, it says this is only available for iPods formatted for Macs.

I then connected it another mac (not the one I'd been using previously) and now the computer won't recognize it! It doesn't show up in finder, on the desktop, or in iTunes. When I plug the iPod into the computer I get the "do not disconnect" message on the iPod screen, but it doesn't show up anywhere on the computer. Also, if the iPod is connected to the computer then iTunes won't load until it is unplugged (w/o ejecting since it won't show up anywhere)
Help! How can I get all my files back?