samsung j330 repair issues

Ive been trying to fix a friends phone, broken screen and dropped in water.I dried it off, fitted new screen, booted up fine. When doing a check of other things I found when trying to use the camera it came up camera failed. I got a replacement, and it still fails so Im at a loss. I tried clearing cache etc, but nothing works.

The second issue it the back and app button dont work. I read they may be susceptible to heat, so I figures they we damaged when the screen was removed. I replaced these, but still nothing. The home button works though.

Can anyone offer some advice?