It’s not the hold switch, because the lock icon still appears and disappears as it should, and it’s not the click wheel, because the click wheel is only responsible for scrolling.
It must be the buttons on the logic board that aren’t working. Make sure that all the buttons on the logic board still have the little black foam circles on them, as the buttons may not get pushed down properly if the foam circles are missing.
If the buttons are being clicked properly, but the iPod still doesn’t respond to them, you may be out of luck. it’s possible that both logic boards got damaged.