Ipad 2 black screen

My friends Ipad 2 was just displaying the empty battery symbol but would not charge or turn on so I put it into DFU mode when it was attached to the computer and itunes recognised it and started to download an update to restore the ipad, however when the update had finished downloading in itunes nothing happened and now the ipad just has a black screen it is not recognised by the computer or itunes and the button combinations don't do anything. I replaced the digitizer, battery and charging port as he dropped it in some water but after putting the new battery in it worked and it would charge but now it is dead. Does anyone know how to bring it back to life without having to replace the logic board as these are only available second hand and are quite expensive