Overheating when connected to iTunes and unresponsive screen

I have bought a second hand phone which was sold as a temperamental screen. I took the phone to a repair shop and they said they had taken it apart and clears all the connectors and put it back together. I took it home as it was working and synced it as a new phone to iTunes .whilst it was doing this I notice it was getting warm especially around the the front facing camera .after the phone had synced I tried to swipe the front screen but no response. Also I've noticed the volume buttons are quite loose could this be the cause.