Can't update or restore

i am trying to restore an iphone 7 but its not working. I have made sure that Itunes for Windows is updated and it has updated the phone but not able to restore and just wondered if there is a problem with the phone and something needs to be replaced. The battery seems to be fine (haven't needed to charge the phone, no swelling) and the screen, although cracked, is working. I can see that someone has opened the phone and the pentalobe screws are missing as well as the brackets for the lower display and front panel sensor assembly connectors but otherwise looks ok. Do you have any suggestions of what might be wrong?