The battery gets older - with or without usage
(sometimes is not using worse than using it)
follow this [guide|427|guide] and disassemble it, look out for possible fluid damage signs (white/greenish stuff on the components), if there are any signs of a fluid damage - clean the logic board with isopropyl alcohol (>90%) and a soft paintbrush - if there aren't any signs of fluids inside the shuffle - take a multimeter (maybe borrow one) and measure the battery - if it's lower than ~ 3.4V the computer won't recognitze the iPod and would not charge it.
the shuffle has a Li-Po cell - they could die within seconds - especially when they wheren't much in use (deep discharging kills Li-Po cells) - if the cell has 0V - you should get a new one