iPod 3rd Gen Classic A1040 (VW Version) charged but doesn't respond

I'm the original owner of the gen 3 iPod that came with my 2003 VW Beetle purchase. Yesterday I was able to use the original docking station and cables to charge the iPod, which hasn't been used for ~20 years. Apple logo displays and I can hear whirring inside the iPod. When I reset it says Ok to Disconnect and I can see in the upper right that the battery is fully charged, but nothing works -- menu doesn't display, no clicks when I press on any of the buttons, no lights. I've tried reset several times, but nothing changes, it goes back to Apple logo display. When I download iTunes on my Windows laptop, the iPod doesn't appear within iTunes, so I haven't been able to try to restore it from there. Since it doesn't sound like a cable/dock/battery issue, what should I try next?