Hi Thomas
i think it is better you can go to a local repaire service guy to identify the root caused: Battery issue/power IC issue/CPU Issue/USB Board.
1. battery issue, it is easy to replace with a battery and fixed it.
2. if it is concern to motherboard, i think it is not easy for you identify it, it maybe need replace with a motherboard.
3. if it is USB Board issue, it will be easy to buy a USB Board.
Thanks
Jack.