Why does my hard drive not have any storage?

If you didn't open it up and replace or fix the internal drive, the thing may be cooked. If your PC recognizes it but your iPod doesn't, then unsure what else to say than do a replacement for the Cable or Drive. As long as you follow the proper guide on the Ifixit site, you should be good. Don't use any metal tools for anything other than opening it up, Lock the device Via the Lock Switch, and then unplug the battery so you don't short it out. I dunno if you can shut the thing down, but if you can, maybe do that? Then you're good to try to fix it. Best case scenario, it's just the drive or Cable and it'll be simple. Worst case, you better hope you have the money to have an onboard repair performed at a Third-Party.

Some tips though, when you unplug the Battery, be careful because of the Small restrictions you need to fit the tweezers into. Also, do not just yank the back plate off because the back isn't a passive locking system for the connectors. Again, you'll wanna look at the guides for this so you know you don't damage your iPod or iPod Classic. Hope this helps, and I hope your iPod works if you fix it!

The iPod drive’s format is likely Apples HFS+ not windows FAT32. This is also why you can’t see the partition. If you have a friend with a Mac system see if they can access it from their system.