Probably a hardware problem. "All" is not lost; you can try to repair it... If it's the hard drive, those parts are no longer produced. You can consider replacing it with commonly available flash-based storage, in the form of compact flash card or SDXC card (on an adapter). This web site relevant information, for 5th gen and later "classic" iPods
https://www.iflash.xyz/
My older iPods (3rd gen and 4th gen) have been "upgraded" with compact flash card and SDXC card (both 64GB), on different adapters. I replaced battery too. They work better now, with much higher storage capacity, than when they were new.
In your case (because it gets stuck at Apple logo), the fault may be something else, such as a problem on logic board. If you end up opening the casing, you should actually disconnect the battery connector (wait a few minutes) and reconnect. Completely remove power from logic board; letting battery drain may not be sufficient.
This web site has illustrated repair guides
https://www.ifixit.com/Device/iPod_Classic
and there are numerous YouTube videos demonstrating opening of iPod classic.