iPhone won't turn on
So I had a friend that dropped his phone in a pool and I put in a new logic board and battery. The phone worked fine, since all damaged parts were removed. Then one day I shut it off, and it wouldn't turn on. I lifted the logic board off the battery, put it back on, and it booted up fine. Now I turned it off again, and even after lifting the connectors apart, it still won't turn back on. Any suggestions on anything I should try?