First of all, I would like to apologize if im on a wrong section or thread. Below are my problem.

Iphone 4s

1.only can turn on when plugged into power socket/power bank or laptop.

2. tried restoring but always comes up with "Error 21"

3. send to shop and the shop said the motherboard faulty.

Is there anyway i can save my iphone 4s now? do i need to change the motherboard? how much does it cost?

all help is very much appreciated.