xperia s shows no signs of life no charging leds nothing

ok so i have a xperia s that is not working i have opened it up and everything seems fine and the battery looks good too. My dad used to own this phone but then one day he put it to charge and it didnt charge and the phone just then died, i have it opened up and have inspected the charge port and it looks good i have even disconnected all the cables and reconnected and still nothing. the charge port looks clean inside and on the board it looks normal aswell. i dont know if its a battery issue or something but one day i had a small samsung battery to try test it and all it did was make the board abit hot but no signs of life. is there a way of fixing without replacing anything?