iPod Classic - Charging doesn't work but syncing do

Hello,

I have a problem with my iPod Classic 6th Gen 80 GB. The charging just doesn't work. I can sync my library with iTunes. iPod shows charging in progress when it is plugged but after unplugging the battery level isn't changed (even after two/three hours). I replaced old battery to the new but problem isn't solved. Can I repair my iPod or it's broken "forever"?

Thanks for all help :)